diff --git a/Meta/Lagom/Fuzzers/FuzzCyrillicDecoder.cpp b/Meta/Lagom/Fuzzers/FuzzCyrillicDecoder.cpp
index 10e3c6e3e6..647dd54020 100644
--- a/Meta/Lagom/Fuzzers/FuzzCyrillicDecoder.cpp
+++ b/Meta/Lagom/Fuzzers/FuzzCyrillicDecoder.cpp
@@ -13,6 +13,6 @@ extern "C" int LLVMFuzzerTestOneInput(uint8_t const* data, size_t size)
 {
     auto decoder = TextCodec::decoder_for("windows-1251"sv);
     VERIFY(decoder.has_value());
-    decoder->to_utf8({ data, size });
+    (void)decoder->to_utf8({ data, size });
     return 0;
 }
diff --git a/Meta/Lagom/Fuzzers/FuzzHebrewDecoder.cpp b/Meta/Lagom/Fuzzers/FuzzHebrewDecoder.cpp
index 866e3b1e61..cfe0873317 100644
--- a/Meta/Lagom/Fuzzers/FuzzHebrewDecoder.cpp
+++ b/Meta/Lagom/Fuzzers/FuzzHebrewDecoder.cpp
@@ -13,6 +13,6 @@ extern "C" int LLVMFuzzerTestOneInput(uint8_t const* data, size_t size)
 {
     auto decoder = TextCodec::decoder_for("windows-1255"sv);
     VERIFY(decoder.has_value());
-    decoder->to_utf8({ data, size });
+    (void)decoder->to_utf8({ data, size });
     return 0;
 }
diff --git a/Meta/Lagom/Fuzzers/FuzzLatin1Decoder.cpp b/Meta/Lagom/Fuzzers/FuzzLatin1Decoder.cpp
index 3a3f03cd90..8a2b667995 100644
--- a/Meta/Lagom/Fuzzers/FuzzLatin1Decoder.cpp
+++ b/Meta/Lagom/Fuzzers/FuzzLatin1Decoder.cpp
@@ -13,6 +13,6 @@ extern "C" int LLVMFuzzerTestOneInput(uint8_t const* data, size_t size)
 {
     auto decoder = TextCodec::decoder_for("windows-1252"sv);
     VERIFY(decoder.has_value());
-    decoder->to_utf8({ data, size });
+    (void)decoder->to_utf8({ data, size });
     return 0;
 }
diff --git a/Meta/Lagom/Fuzzers/FuzzLatin2Decoder.cpp b/Meta/Lagom/Fuzzers/FuzzLatin2Decoder.cpp
index 1d83a83920..3fb16d631e 100644
--- a/Meta/Lagom/Fuzzers/FuzzLatin2Decoder.cpp
+++ b/Meta/Lagom/Fuzzers/FuzzLatin2Decoder.cpp
@@ -13,6 +13,6 @@ extern "C" int LLVMFuzzerTestOneInput(uint8_t const* data, size_t size)
 {
     auto decoder = TextCodec::decoder_for("iso-8859-2"sv);
     VERIFY(decoder.has_value());
-    decoder->to_utf8({ data, size });
+    (void)decoder->to_utf8({ data, size });
     return 0;
 }
diff --git a/Meta/Lagom/Fuzzers/FuzzUTF16BEDecoder.cpp b/Meta/Lagom/Fuzzers/FuzzUTF16BEDecoder.cpp
index 26b2205549..a24fb5e8e3 100644
--- a/Meta/Lagom/Fuzzers/FuzzUTF16BEDecoder.cpp
+++ b/Meta/Lagom/Fuzzers/FuzzUTF16BEDecoder.cpp
@@ -13,6 +13,6 @@ extern "C" int LLVMFuzzerTestOneInput(uint8_t const* data, size_t size)
 {
     auto decoder = TextCodec::decoder_for("utf-16be"sv);
     VERIFY(decoder.has_value());
-    decoder->to_utf8({ data, size });
+    (void)decoder->to_utf8({ data, size });
     return 0;
 }
diff --git a/Tests/LibTextCodec/TestTextDecoders.cpp b/Tests/LibTextCodec/TestTextDecoders.cpp
index fe873bf7ff..d1658d337c 100644
--- a/Tests/LibTextCodec/TestTextDecoders.cpp
+++ b/Tests/LibTextCodec/TestTextDecoders.cpp
@@ -4,6 +4,7 @@
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
+#include <AK/String.h>
 #include <AK/Vector.h>
 #include <LibTest/TestCase.h>
 #include <LibTextCodec/Decoder.h>
@@ -15,13 +16,13 @@ TEST_CASE(test_utf8_decode)
     auto test_string = "\xf0\x9f\x98\x80"sv;
 
     Vector<u32> processed_code_points;
-    decoder.process(test_string, [&](u32 code_point) {
-        processed_code_points.append(code_point);
-    });
+    MUST(decoder.process(test_string, [&](u32 code_point) {
+        return processed_code_points.try_append(code_point);
+    }));
     EXPECT(processed_code_points.size() == 1);
     EXPECT(processed_code_points[0] == 0x1F600);
 
-    EXPECT(decoder.to_utf8(test_string) == test_string);
+    EXPECT(MUST(decoder.to_utf8(test_string)) == test_string);
 }
 
 TEST_CASE(test_utf16be_decode)
@@ -31,9 +32,9 @@ TEST_CASE(test_utf16be_decode)
     auto test_string = "\x00s\x00\xe4\x00k\xd8=\xde\x00"sv;
 
     Vector<u32> processed_code_points;
-    decoder.process(test_string, [&](u32 code_point) {
-        processed_code_points.append(code_point);
-    });
+    MUST(decoder.process(test_string, [&](u32 code_point) {
+        return processed_code_points.try_append(code_point);
+    }));
     EXPECT(processed_code_points.size() == 4);
     EXPECT(processed_code_points[0] == 0x73);
     EXPECT(processed_code_points[1] == 0xE4);
@@ -48,9 +49,9 @@ TEST_CASE(test_utf16le_decode)
     auto test_string = "s\x00\xe4\x00k\x00=\xd8\x00\xde"sv;
 
     Vector<u32> processed_code_points;
-    decoder.process(test_string, [&](u32 code_point) {
-        processed_code_points.append(code_point);
-    });
+    MUST(decoder.process(test_string, [&](u32 code_point) {
+        return processed_code_points.try_append(code_point);
+    }));
     EXPECT(processed_code_points.size() == 4);
     EXPECT(processed_code_points[0] == 0x73);
     EXPECT(processed_code_points[1] == 0xE4);
diff --git a/Userland/Applications/HexEditor/HexEditorWidget.cpp b/Userland/Applications/HexEditor/HexEditorWidget.cpp
index 5feae61de1..2869195bc4 100644
--- a/Userland/Applications/HexEditor/HexEditorWidget.cpp
+++ b/Userland/Applications/HexEditor/HexEditorWidget.cpp
@@ -392,7 +392,7 @@ void HexEditorWidget::update_inspector_values(size_t position)
 
     // FIXME: Parse as other values like Timestamp etc
 
-    DeprecatedString utf16_string = TextCodec::decoder_for("utf-16le"sv)->to_utf8(StringView(selected_bytes.span()));
+    DeprecatedString utf16_string = TextCodec::decoder_for("utf-16le"sv)->to_utf8(StringView(selected_bytes.span())).release_value_but_fixme_should_propagate_errors().to_deprecated_string();
     value_inspector_model->set_parsed_value(ValueInspectorModel::ValueType::UTF16String, utf16_string);
 
     m_value_inspector->set_model(value_inspector_model);
diff --git a/Userland/Libraries/LibGfx/Font/OpenType/Font.cpp b/Userland/Libraries/LibGfx/Font/OpenType/Font.cpp
index 3a983ee213..78983fca08 100644
--- a/Userland/Libraries/LibGfx/Font/OpenType/Font.cpp
+++ b/Userland/Libraries/LibGfx/Font/OpenType/Font.cpp
@@ -322,7 +322,7 @@ DeprecatedString Name::string_for_id(NameId id) const
 
     if (platform_id == to_underlying(Platform::Windows)) {
         static auto& decoder = *TextCodec::decoder_for("utf-16be"sv);
-        return decoder.to_utf8(StringView { (char const*)m_slice.offset_pointer(storage_offset + offset), length });
+        return decoder.to_utf8(StringView { (char const*)m_slice.offset_pointer(storage_offset + offset), length }).release_value_but_fixme_should_propagate_errors().to_deprecated_string();
     }
 
     return DeprecatedString((char const*)m_slice.offset_pointer(storage_offset + offset), length);
diff --git a/Userland/Libraries/LibGfx/ICC/TagTypes.cpp b/Userland/Libraries/LibGfx/ICC/TagTypes.cpp
index c777e3166a..a494c1a16d 100644
--- a/Userland/Libraries/LibGfx/ICC/TagTypes.cpp
+++ b/Userland/Libraries/LibGfx/ICC/TagTypes.cpp
@@ -703,7 +703,7 @@ ErrorOr<NonnullRefPtr<MultiLocalizedUnicodeTagData>> MultiLocalizedUnicodeTagDat
             return Error::from_string_literal("ICC::Profile: multiLocalizedUnicodeType string offset out of bounds");
 
         StringView utf_16be_data { bytes.data() + record.string_offset_in_bytes, record.string_length_in_bytes };
-        records[i].text = TRY(String::from_deprecated_string(utf_16be_decoder.to_utf8(utf_16be_data)));
+        records[i].text = TRY(utf_16be_decoder.to_utf8(utf_16be_data));
     }
 
     return try_make_ref_counted<MultiLocalizedUnicodeTagData>(offset, size, move(records));
@@ -955,7 +955,7 @@ ErrorOr<NonnullRefPtr<TextDescriptionTagData>> TextDescriptionTagData::from_byte
             return Error::from_string_literal("ICC::Profile: textDescriptionType Unicode description not \\0-terminated");
 
         StringView utf_16be_data { unicode_description_data, byte_size_without_nul };
-        unicode_description = TRY(String::from_deprecated_string(TextCodec::decoder_for("utf-16be"sv)->to_utf8(utf_16be_data)));
+        unicode_description = TRY(TextCodec::decoder_for("utf-16be"sv)->to_utf8(utf_16be_data));
     }
 
     // ScriptCode
@@ -1001,7 +1001,7 @@ ErrorOr<NonnullRefPtr<TextDescriptionTagData>> TextDescriptionTagData::from_byte
             if (macintosh_description_data[macintosh_description_length - 1] != '\0')
                 return Error::from_string_literal("ICC::Profile: textDescriptionType ScriptCode not \\0-terminated");
 
-            macintosh_description = TRY(String::from_deprecated_string(TextCodec::decoder_for("x-mac-roman"sv)->to_utf8({ macintosh_description_data, (size_t)macintosh_description_length - 1 })));
+            macintosh_description = TRY(TextCodec::decoder_for("x-mac-roman"sv)->to_utf8({ macintosh_description_data, (size_t)macintosh_description_length - 1 }));
         } else {
             dbgln("TODO: ICCProfile textDescriptionType ScriptCode {}, length {}", scriptcode_code, macintosh_description_length);
         }
diff --git a/Userland/Libraries/LibPDF/Parser.cpp b/Userland/Libraries/LibPDF/Parser.cpp
index c6ade6bac6..4f90d06471 100644
--- a/Userland/Libraries/LibPDF/Parser.cpp
+++ b/Userland/Libraries/LibPDF/Parser.cpp
@@ -267,7 +267,7 @@ NonnullRefPtr<StringObject> Parser::parse_string()
 
     if (unencrypted_string.bytes().starts_with(Array<u8, 2> { 0xfe, 0xff })) {
         // The string is encoded in UTF16-BE
-        string_object->set_string(TextCodec::decoder_for("utf-16be"sv)->to_utf8(unencrypted_string));
+        string_object->set_string(TextCodec::decoder_for("utf-16be"sv)->to_utf8(unencrypted_string).release_value_but_fixme_should_propagate_errors().to_deprecated_string());
     } else if (unencrypted_string.bytes().starts_with(Array<u8, 3> { 239, 187, 191 })) {
         // The string is encoded in UTF-8. This is the default anyways, but if these bytes
         // are explicitly included, we have to trim them
diff --git a/Userland/Libraries/LibTextCodec/Decoder.cpp b/Userland/Libraries/LibTextCodec/Decoder.cpp
index 14b4acd155..79c3d8f760 100644
--- a/Userland/Libraries/LibTextCodec/Decoder.cpp
+++ b/Userland/Libraries/LibTextCodec/Decoder.cpp
@@ -6,7 +6,6 @@
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
-#include <AK/DeprecatedString.h>
 #include <AK/StringBuilder.h>
 #include <AK/Utf16View.h>
 #include <AK/Utf8View.h>
@@ -197,7 +196,7 @@ Optional<Decoder&> bom_sniff_to_decoder(StringView input)
 }
 
 // https://encoding.spec.whatwg.org/#decode
-DeprecatedString convert_input_to_utf8_using_given_decoder_unless_there_is_a_byte_order_mark(Decoder& fallback_decoder, StringView input)
+ErrorOr<String> convert_input_to_utf8_using_given_decoder_unless_there_is_a_byte_order_mark(Decoder& fallback_decoder, StringView input)
 {
     Decoder* actual_decoder = &fallback_decoder;
 
@@ -220,21 +219,22 @@ DeprecatedString convert_input_to_utf8_using_given_decoder_unless_there_is_a_byt
     return actual_decoder->to_utf8(input);
 }
 
-DeprecatedString Decoder::to_utf8(StringView input)
+ErrorOr<String> Decoder::to_utf8(StringView input)
 {
     StringBuilder builder(input.length());
-    process(input, [&builder](u32 c) { builder.append_code_point(c); });
-    return builder.to_deprecated_string();
+    TRY(process(input, [&builder](u32 c) { return builder.try_append_code_point(c); }));
+    return builder.to_string();
 }
 
-void UTF8Decoder::process(StringView input, Function<void(u32)> on_code_point)
+ErrorOr<void> UTF8Decoder::process(StringView input, Function<ErrorOr<void>(u32)> on_code_point)
 {
     for (auto c : Utf8View(input)) {
-        on_code_point(c);
+        TRY(on_code_point(c));
     }
+    return {};
 }
 
-DeprecatedString UTF8Decoder::to_utf8(StringView input)
+ErrorOr<String> UTF8Decoder::to_utf8(StringView input)
 {
     // Discard the BOM
     auto bomless_input = input;
@@ -242,10 +242,10 @@ DeprecatedString UTF8Decoder::to_utf8(StringView input)
         bomless_input = input.substring_view(3);
     }
 
-    return bomless_input;
+    return String::from_utf8(bomless_input);
 }
 
-void UTF16BEDecoder::process(StringView input, Function<void(u32)> on_code_point)
+ErrorOr<void> UTF16BEDecoder::process(StringView input, Function<ErrorOr<void>(u32)> on_code_point)
 {
     // rfc2781, 2.2 Decoding UTF-16
     size_t utf16_length = input.length() - (input.length() % 2);
@@ -254,7 +254,7 @@ void UTF16BEDecoder::process(StringView input, Function<void(u32)> on_code_point
         //    of W1. Terminate.
         u16 w1 = (static_cast<u8>(input[i]) << 8) | static_cast<u8>(input[i + 1]);
         if (!is_unicode_surrogate(w1)) {
-            on_code_point(w1);
+            TRY(on_code_point(w1));
             continue;
         }
 
@@ -265,13 +265,13 @@ void UTF16BEDecoder::process(StringView input, Function<void(u32)> on_code_point
         //    is not between 0xDC00 and 0xDFFF, the sequence is in error.
         //    Terminate.
         if (!Utf16View::is_high_surrogate(w1) || i + 2 == utf16_length) {
-            on_code_point(replacement_code_point);
+            TRY(on_code_point(replacement_code_point));
             continue;
         }
 
         u16 w2 = (static_cast<u8>(input[i + 2]) << 8) | static_cast<u8>(input[i + 3]);
         if (!Utf16View::is_low_surrogate(w2)) {
-            on_code_point(replacement_code_point);
+            TRY(on_code_point(replacement_code_point));
             continue;
         }
 
@@ -279,12 +279,14 @@ void UTF16BEDecoder::process(StringView input, Function<void(u32)> on_code_point
         //    bits of W1 as its 10 high-order bits and the 10 low-order bits of
         //    W2 as its 10 low-order bits.
         // 5) Add 0x10000 to U' to obtain the character value U. Terminate.
-        on_code_point(Utf16View::decode_surrogate_pair(w1, w2));
+        TRY(on_code_point(Utf16View::decode_surrogate_pair(w1, w2)));
         i += 2;
     }
+
+    return {};
 }
 
-DeprecatedString UTF16BEDecoder::to_utf8(StringView input)
+ErrorOr<String> UTF16BEDecoder::to_utf8(StringView input)
 {
     // Discard the BOM
     auto bomless_input = input;
@@ -292,11 +294,11 @@ DeprecatedString UTF16BEDecoder::to_utf8(StringView input)
         bomless_input = input.substring_view(2);
 
     StringBuilder builder(bomless_input.length() / 2);
-    process(bomless_input, [&builder](u32 c) { builder.append_code_point(c); });
-    return builder.to_deprecated_string();
+    TRY(process(bomless_input, [&builder](u32 c) { return builder.try_append_code_point(c); }));
+    return builder.to_string();
 }
 
-void UTF16LEDecoder::process(StringView input, Function<void(u32)> on_code_point)
+ErrorOr<void> UTF16LEDecoder::process(StringView input, Function<ErrorOr<void>(u32)> on_code_point)
 {
     // rfc2781, 2.2 Decoding UTF-16
     size_t utf16_length = input.length() - (input.length() % 2);
@@ -305,7 +307,7 @@ void UTF16LEDecoder::process(StringView input, Function<void(u32)> on_code_point
         //    of W1. Terminate.
         u16 w1 = static_cast<u8>(input[i]) | (static_cast<u8>(input[i + 1]) << 8);
         if (!is_unicode_surrogate(w1)) {
-            on_code_point(w1);
+            TRY(on_code_point(w1));
             continue;
         }
 
@@ -316,13 +318,13 @@ void UTF16LEDecoder::process(StringView input, Function<void(u32)> on_code_point
         //    is not between 0xDC00 and 0xDFFF, the sequence is in error.
         //    Terminate.
         if (!Utf16View::is_high_surrogate(w1) || i + 2 == utf16_length) {
-            on_code_point(replacement_code_point);
+            TRY(on_code_point(replacement_code_point));
             continue;
         }
 
         u16 w2 = static_cast<u8>(input[i + 2]) | (static_cast<u8>(input[i + 3]) << 8);
         if (!Utf16View::is_low_surrogate(w2)) {
-            on_code_point(replacement_code_point);
+            TRY(on_code_point(replacement_code_point));
             continue;
         }
 
@@ -330,12 +332,14 @@ void UTF16LEDecoder::process(StringView input, Function<void(u32)> on_code_point
         //    bits of W1 as its 10 high-order bits and the 10 low-order bits of
         //    W2 as its 10 low-order bits.
         // 5) Add 0x10000 to U' to obtain the character value U. Terminate.
-        on_code_point(Utf16View::decode_surrogate_pair(w1, w2));
+        TRY(on_code_point(Utf16View::decode_surrogate_pair(w1, w2)));
         i += 2;
     }
+
+    return {};
 }
 
-DeprecatedString UTF16LEDecoder::to_utf8(StringView input)
+ErrorOr<String> UTF16LEDecoder::to_utf8(StringView input)
 {
     // Discard the BOM
     auto bomless_input = input;
@@ -343,16 +347,18 @@ DeprecatedString UTF16LEDecoder::to_utf8(StringView input)
         bomless_input = input.substring_view(2);
 
     StringBuilder builder(bomless_input.length() / 2);
-    process(bomless_input, [&builder](u32 c) { builder.append_code_point(c); });
-    return builder.to_deprecated_string();
+    TRY(process(bomless_input, [&builder](u32 c) { return builder.try_append_code_point(c); }));
+    return builder.to_string();
 }
 
-void Latin1Decoder::process(StringView input, Function<void(u32)> on_code_point)
+ErrorOr<void> Latin1Decoder::process(StringView input, Function<ErrorOr<void>(u32)> on_code_point)
 {
     for (auto ch : input) {
         // Latin1 is the same as the first 256 Unicode code_points, so no mapping is needed, just utf-8 encoding.
-        on_code_point(ch);
+        TRY(on_code_point(ch));
     }
+
+    return {};
 }
 
 namespace {
@@ -434,14 +440,16 @@ u32 convert_latin2_to_utf8(u8 in)
 }
 }
 
-void Latin2Decoder::process(StringView input, Function<void(u32)> on_code_point)
+ErrorOr<void> Latin2Decoder::process(StringView input, Function<ErrorOr<void>(u32)> on_code_point)
 {
     for (auto c : input) {
-        on_code_point(convert_latin2_to_utf8(c));
+        TRY(on_code_point(convert_latin2_to_utf8(c)));
     }
+
+    return {};
 }
 
-void HebrewDecoder::process(StringView input, Function<void(u32)> on_code_point)
+ErrorOr<void> HebrewDecoder::process(StringView input, Function<ErrorOr<void>(u32)> on_code_point)
 {
     static constexpr Array<u32, 128> translation_table = {
         0x20AC, 0xFFFD, 0x201A, 0x192, 0x201E, 0x2026, 0x2020, 0x2021, 0x2C6, 0x2030, 0xFFFD, 0x2039, 0xFFFD, 0xFFFD, 0xFFFD, 0xFFFD,
@@ -455,14 +463,16 @@ void HebrewDecoder::process(StringView input, Function<void(u32)> on_code_point)
     };
     for (unsigned char ch : input) {
         if (ch < 0x80) { // Superset of ASCII
-            on_code_point(ch);
+            TRY(on_code_point(ch));
         } else {
-            on_code_point(translation_table[ch - 0x80]);
+            TRY(on_code_point(translation_table[ch - 0x80]));
         }
     }
+
+    return {};
 }
 
-void CyrillicDecoder::process(StringView input, Function<void(u32)> on_code_point)
+ErrorOr<void> CyrillicDecoder::process(StringView input, Function<ErrorOr<void>(u32)> on_code_point)
 {
     static constexpr Array<u32, 128> translation_table = {
         0x402, 0x403, 0x201A, 0x453, 0x201E, 0x2026, 0x2020, 0x2021, 0x20AC, 0x2030, 0x409, 0x2039, 0x40A, 0x40C, 0x40B, 0x40F,
@@ -476,14 +486,16 @@ void CyrillicDecoder::process(StringView input, Function<void(u32)> on_code_poin
     };
     for (unsigned char ch : input) {
         if (ch < 0x80) { // Superset of ASCII
-            on_code_point(ch);
+            TRY(on_code_point(ch));
         } else {
-            on_code_point(translation_table[ch - 0x80]);
+            TRY(on_code_point(translation_table[ch - 0x80]));
         }
     }
+
+    return {};
 }
 
-void Koi8RDecoder::process(StringView input, Function<void(u32)> on_code_point)
+ErrorOr<void> Koi8RDecoder::process(StringView input, Function<ErrorOr<void>(u32)> on_code_point)
 {
     // clang-format off
     static constexpr Array<u32, 128> translation_table = {
@@ -500,14 +512,16 @@ void Koi8RDecoder::process(StringView input, Function<void(u32)> on_code_point)
 
     for (unsigned char ch : input) {
         if (ch < 0x80) { // Superset of ASCII
-            on_code_point(ch);
+            TRY(on_code_point(ch));
         } else {
-            on_code_point(translation_table[ch - 0x80]);
+            TRY(on_code_point(translation_table[ch - 0x80]));
         }
     }
+
+    return {};
 }
 
-void Latin9Decoder::process(StringView input, Function<void(u32)> on_code_point)
+ErrorOr<void> Latin9Decoder::process(StringView input, Function<ErrorOr<void>(u32)> on_code_point)
 {
     auto convert_latin9_to_utf8 = [](u8 ch) -> u32 {
         // Latin9 is the same as the first 256 Unicode code points, except for 8 characters.
@@ -534,11 +548,13 @@ void Latin9Decoder::process(StringView input, Function<void(u32)> on_code_point)
     };
 
     for (auto ch : input) {
-        on_code_point(convert_latin9_to_utf8(ch));
+        TRY(on_code_point(convert_latin9_to_utf8(ch)));
     }
+
+    return {};
 }
 
-void MacRomanDecoder::process(StringView input, Function<void(u32)> on_code_point)
+ErrorOr<void> MacRomanDecoder::process(StringView input, Function<ErrorOr<void>(u32)> on_code_point)
 {
     // https://encoding.spec.whatwg.org/index-macintosh.txt
     // clang-format off
@@ -556,14 +572,16 @@ void MacRomanDecoder::process(StringView input, Function<void(u32)> on_code_poin
 
     for (u8 ch : input) {
         if (ch < 0x80) { // Superset of ASCII
-            on_code_point(ch);
+            TRY(on_code_point(ch));
         } else {
-            on_code_point(translation_table[ch - 0x80]);
+            TRY(on_code_point(translation_table[ch - 0x80]));
         }
     }
+
+    return {};
 }
 
-void TurkishDecoder::process(StringView input, Function<void(u32)> on_code_point)
+ErrorOr<void> TurkishDecoder::process(StringView input, Function<ErrorOr<void>(u32)> on_code_point)
 {
     auto convert_turkish_to_utf8 = [](u8 ch) -> u32 {
         // Turkish (aka ISO-8859-9, Windows-1254) is the same as the first 256 Unicode code points, except for 6 characters.
@@ -586,12 +604,14 @@ void TurkishDecoder::process(StringView input, Function<void(u32)> on_code_point
     };
 
     for (auto ch : input) {
-        on_code_point(convert_turkish_to_utf8(ch));
+        TRY(on_code_point(convert_turkish_to_utf8(ch)));
     }
+
+    return {};
 }
 
 // https://encoding.spec.whatwg.org/#x-user-defined-decoder
-void XUserDefinedDecoder::process(StringView input, Function<void(u32)> on_code_point)
+ErrorOr<void> XUserDefinedDecoder::process(StringView input, Function<ErrorOr<void>(u32)> on_code_point)
 {
     auto convert_x_user_defined_to_utf8 = [](u8 ch) -> u32 {
         // 2. If byte is an ASCII byte, return a code point whose value is byte.
@@ -606,10 +626,12 @@ void XUserDefinedDecoder::process(StringView input, Function<void(u32)> on_code_
     };
 
     for (auto ch : input) {
-        on_code_point(convert_x_user_defined_to_utf8(ch));
+        TRY(on_code_point(convert_x_user_defined_to_utf8(ch)));
     }
 
     // 1. If byte is end-of-queue, return finished.
+
+    return {};
 }
 
 }
diff --git a/Userland/Libraries/LibTextCodec/Decoder.h b/Userland/Libraries/LibTextCodec/Decoder.h
index 6ab41556b5..c678677bf5 100644
--- a/Userland/Libraries/LibTextCodec/Decoder.h
+++ b/Userland/Libraries/LibTextCodec/Decoder.h
@@ -11,13 +11,14 @@
 #include <AK/Forward.h>
 #include <AK/Function.h>
 #include <AK/Optional.h>
+#include <AK/String.h>
 
 namespace TextCodec {
 
 class Decoder {
 public:
-    virtual void process(StringView, Function<void(u32)> on_code_point) = 0;
-    virtual DeprecatedString to_utf8(StringView);
+    virtual ErrorOr<void> process(StringView, Function<ErrorOr<void>(u32)> on_code_point) = 0;
+    virtual ErrorOr<String> to_utf8(StringView);
 
 protected:
     virtual ~Decoder() = default;
@@ -25,65 +26,65 @@ protected:
 
 class UTF8Decoder final : public Decoder {
 public:
-    virtual void process(StringView, Function<void(u32)> on_code_point) override;
-    virtual DeprecatedString to_utf8(StringView) override;
+    virtual ErrorOr<void> process(StringView, Function<ErrorOr<void>(u32)> on_code_point) override;
+    virtual ErrorOr<String> to_utf8(StringView) override;
 };
 
 class UTF16BEDecoder final : public Decoder {
 public:
-    virtual void process(StringView, Function<void(u32)> on_code_point) override;
-    virtual DeprecatedString to_utf8(StringView) override;
+    virtual ErrorOr<void> process(StringView, Function<ErrorOr<void>(u32)> on_code_point) override;
+    virtual ErrorOr<String> to_utf8(StringView) override;
 };
 
 class UTF16LEDecoder final : public Decoder {
 public:
-    virtual void process(StringView, Function<void(u32)> on_code_point) override;
-    virtual DeprecatedString to_utf8(StringView) override;
+    virtual ErrorOr<void> process(StringView, Function<ErrorOr<void>(u32)> on_code_point) override;
+    virtual ErrorOr<String> to_utf8(StringView) override;
 };
 
 class Latin1Decoder final : public Decoder {
 public:
-    virtual void process(StringView, Function<void(u32)> on_code_point) override;
+    virtual ErrorOr<void> process(StringView, Function<ErrorOr<void>(u32)> on_code_point) override;
 };
 
 class Latin2Decoder final : public Decoder {
 public:
-    virtual void process(StringView, Function<void(u32)> on_code_point) override;
+    virtual ErrorOr<void> process(StringView, Function<ErrorOr<void>(u32)> on_code_point) override;
 };
 
 class HebrewDecoder final : public Decoder {
 public:
-    virtual void process(StringView, Function<void(u32)> on_code_point) override;
+    virtual ErrorOr<void> process(StringView, Function<ErrorOr<void>(u32)> on_code_point) override;
 };
 
 class CyrillicDecoder final : public Decoder {
 public:
-    virtual void process(StringView, Function<void(u32)> on_code_point) override;
+    virtual ErrorOr<void> process(StringView, Function<ErrorOr<void>(u32)> on_code_point) override;
 };
 
 class Koi8RDecoder final : public Decoder {
 public:
-    virtual void process(StringView, Function<void(u32)> on_code_point) override;
+    virtual ErrorOr<void> process(StringView, Function<ErrorOr<void>(u32)> on_code_point) override;
 };
 
 class Latin9Decoder final : public Decoder {
 public:
-    virtual void process(StringView, Function<void(u32)> on_code_point) override;
+    virtual ErrorOr<void> process(StringView, Function<ErrorOr<void>(u32)> on_code_point) override;
 };
 
 class MacRomanDecoder final : public Decoder {
 public:
-    virtual void process(StringView, Function<void(u32)> on_code_point) override;
+    virtual ErrorOr<void> process(StringView, Function<ErrorOr<void>(u32)> on_code_point) override;
 };
 
 class TurkishDecoder final : public Decoder {
 public:
-    virtual void process(StringView, Function<void(u32)> on_code_point) override;
+    virtual ErrorOr<void> process(StringView, Function<ErrorOr<void>(u32)> on_code_point) override;
 };
 
 class XUserDefinedDecoder final : public Decoder {
 public:
-    virtual void process(StringView, Function<void(u32)> on_code_point) override;
+    virtual ErrorOr<void> process(StringView, Function<ErrorOr<void>(u32)> on_code_point) override;
 };
 
 Optional<Decoder&> decoder_for(StringView encoding);
@@ -94,6 +95,6 @@ Optional<Decoder&> bom_sniff_to_decoder(StringView);
 
 // NOTE: This has an obnoxious name to discourage usage. Only use this if you absolutely must! For example, XHR in LibWeb uses this.
 // This will use the given decoder unless there is a byte order mark in the input, in which we will instead use the appropriate Unicode decoder.
-DeprecatedString convert_input_to_utf8_using_given_decoder_unless_there_is_a_byte_order_mark(Decoder&, StringView);
+ErrorOr<String> convert_input_to_utf8_using_given_decoder_unless_there_is_a_byte_order_mark(Decoder&, StringView);
 
 }
diff --git a/Userland/Libraries/LibWeb/CSS/Parser/Tokenizer.cpp b/Userland/Libraries/LibWeb/CSS/Parser/Tokenizer.cpp
index 8cb69ab0c7..f808bbaea7 100644
--- a/Userland/Libraries/LibWeb/CSS/Parser/Tokenizer.cpp
+++ b/Userland/Libraries/LibWeb/CSS/Parser/Tokenizer.cpp
@@ -206,37 +206,39 @@ Tokenizer::Tokenizer(StringView input, StringView encoding)
         bool last_was_carriage_return = false;
 
         // To filter code points from a stream of (unfiltered) code points input:
-        decoder->process(input, [&builder, &last_was_carriage_return](u32 code_point) {
-            // Replace any U+000D CARRIAGE RETURN (CR) code points,
-            // U+000C FORM FEED (FF) code points,
-            // or pairs of U+000D CARRIAGE RETURN (CR) followed by U+000A LINE FEED (LF)
-            // in input by a single U+000A LINE FEED (LF) code point.
-            if (code_point == '\r') {
-                if (last_was_carriage_return) {
-                    builder.append('\n');
-                } else {
-                    last_was_carriage_return = true;
-                }
-            } else {
-                if (last_was_carriage_return)
-                    builder.append('\n');
+        decoder->process(input, [&builder, &last_was_carriage_return](u32 code_point) -> ErrorOr<void> {
+                   // Replace any U+000D CARRIAGE RETURN (CR) code points,
+                   // U+000C FORM FEED (FF) code points,
+                   // or pairs of U+000D CARRIAGE RETURN (CR) followed by U+000A LINE FEED (LF)
+                   // in input by a single U+000A LINE FEED (LF) code point.
+                   if (code_point == '\r') {
+                       if (last_was_carriage_return) {
+                           TRY(builder.try_append('\n'));
+                       } else {
+                           last_was_carriage_return = true;
+                       }
+                   } else {
+                       if (last_was_carriage_return)
+                           TRY(builder.try_append('\n'));
 
-                if (code_point == '\n') {
-                    if (!last_was_carriage_return)
-                        builder.append('\n');
+                       if (code_point == '\n') {
+                           if (!last_was_carriage_return)
+                               TRY(builder.try_append('\n'));
 
-                } else if (code_point == '\f') {
-                    builder.append('\n');
-                    // Replace any U+0000 NULL or surrogate code points in input with U+FFFD REPLACEMENT CHARACTER (�).
-                } else if (code_point == 0x00 || (code_point >= 0xD800 && code_point <= 0xDFFF)) {
-                    builder.append_code_point(REPLACEMENT_CHARACTER);
-                } else {
-                    builder.append_code_point(code_point);
-                }
+                       } else if (code_point == '\f') {
+                           TRY(builder.try_append('\n'));
+                           // Replace any U+0000 NULL or surrogate code points in input with U+FFFD REPLACEMENT CHARACTER (�).
+                       } else if (code_point == 0x00 || (code_point >= 0xD800 && code_point <= 0xDFFF)) {
+                           TRY(builder.try_append_code_point(REPLACEMENT_CHARACTER));
+                       } else {
+                           TRY(builder.try_append_code_point(code_point));
+                       }
 
-                last_was_carriage_return = false;
-            }
-        });
+                       last_was_carriage_return = false;
+                   }
+                   return {};
+               })
+            .release_value_but_fixme_should_propagate_errors();
         return builder.to_string();
     };
 
diff --git a/Userland/Libraries/LibWeb/Encoding/TextDecoder.cpp b/Userland/Libraries/LibWeb/Encoding/TextDecoder.cpp
index af2cce78aa..1420352dbc 100644
--- a/Userland/Libraries/LibWeb/Encoding/TextDecoder.cpp
+++ b/Userland/Libraries/LibWeb/Encoding/TextDecoder.cpp
@@ -50,7 +50,7 @@ WebIDL::ExceptionOr<DeprecatedString> TextDecoder::decode(JS::Handle<JS::Object>
     if (data_buffer_or_error.is_error())
         return WebIDL::OperationError::create(realm(), "Failed to copy bytes from ArrayBuffer");
     auto& data_buffer = data_buffer_or_error.value();
-    return m_decoder.to_utf8({ data_buffer.data(), data_buffer.size() });
+    return TRY_OR_THROW_OOM(vm(), m_decoder.to_utf8({ data_buffer.data(), data_buffer.size() }));
 }
 
 }
diff --git a/Userland/Libraries/LibWeb/HTML/HTMLScriptElement.cpp b/Userland/Libraries/LibWeb/HTML/HTMLScriptElement.cpp
index b3904a5d84..8b9943944c 100644
--- a/Userland/Libraries/LibWeb/HTML/HTMLScriptElement.cpp
+++ b/Userland/Libraries/LibWeb/HTML/HTMLScriptElement.cpp
@@ -515,7 +515,7 @@ void HTMLScriptElement::resource_did_load()
     // we have to re-encode it to UTF-8.
     if (resource()->has_encoding()) {
         if (auto codec = TextCodec::decoder_for(resource()->encoding().value()); codec.has_value()) {
-            data = codec->to_utf8(data).to_byte_buffer();
+            data = codec->to_utf8(data).release_value_but_fixme_should_propagate_errors().to_deprecated_string().to_byte_buffer();
         }
     }
 
diff --git a/Userland/Libraries/LibWeb/HTML/Parser/HTMLTokenizer.cpp b/Userland/Libraries/LibWeb/HTML/Parser/HTMLTokenizer.cpp
index 3dfd4e3274..f661ee6f80 100644
--- a/Userland/Libraries/LibWeb/HTML/Parser/HTMLTokenizer.cpp
+++ b/Userland/Libraries/LibWeb/HTML/Parser/HTMLTokenizer.cpp
@@ -2800,7 +2800,7 @@ HTMLTokenizer::HTMLTokenizer(StringView input, DeprecatedString const& encoding)
 {
     auto decoder = TextCodec::decoder_for(encoding);
     VERIFY(decoder.has_value());
-    m_decoded_input = decoder->to_utf8(input);
+    m_decoded_input = decoder->to_utf8(input).release_value_but_fixme_should_propagate_errors().to_deprecated_string();
     m_utf8_view = Utf8View(m_decoded_input);
     m_utf8_iterator = m_utf8_view.begin();
     m_prev_utf8_iterator = m_utf8_view.begin();
diff --git a/Userland/Libraries/LibWeb/HTML/Window.cpp b/Userland/Libraries/LibWeb/HTML/Window.cpp
index 1edac12573..c03b9e7425 100644
--- a/Userland/Libraries/LibWeb/HTML/Window.cpp
+++ b/Userland/Libraries/LibWeb/HTML/Window.cpp
@@ -1421,9 +1421,9 @@ JS_DEFINE_NATIVE_FUNCTION(Window::atob)
     // NOTE: Any 8-bit encoding -> utf-8 decoder will work for this
     auto text_decoder = TextCodec::decoder_for("windows-1252"sv);
     VERIFY(text_decoder.has_value());
-    auto text = text_decoder->to_utf8(decoded.release_value());
+    auto text = TRY_OR_THROW_OOM(vm, text_decoder->to_utf8(decoded.release_value()));
 
-    return JS::PrimitiveString::create(vm, DeprecatedString(text));
+    return JS::PrimitiveString::create(vm, text);
 }
 
 JS_DEFINE_NATIVE_FUNCTION(Window::btoa)
diff --git a/Userland/Libraries/LibWeb/HTML/WorkerGlobalScope.cpp b/Userland/Libraries/LibWeb/HTML/WorkerGlobalScope.cpp
index c31c8982b1..e600860285 100644
--- a/Userland/Libraries/LibWeb/HTML/WorkerGlobalScope.cpp
+++ b/Userland/Libraries/LibWeb/HTML/WorkerGlobalScope.cpp
@@ -163,7 +163,7 @@ WebIDL::ExceptionOr<DeprecatedString> WorkerGlobalScope::atob(DeprecatedString c
     // decode_base64() returns a byte string. LibJS uses UTF-8 for strings. Use Latin1Decoder to convert bytes 128-255 to UTF-8.
     auto decoder = TextCodec::decoder_for("windows-1252"sv);
     VERIFY(decoder.has_value());
-    return decoder->to_utf8(decoded_data.value());
+    return TRY_OR_THROW_OOM(vm(), decoder->to_utf8(decoded_data.value()));
 }
 
 }
diff --git a/Userland/Libraries/LibWeb/Infra/JSON.cpp b/Userland/Libraries/LibWeb/Infra/JSON.cpp
index 5bc079c626..05d73c5dfc 100644
--- a/Userland/Libraries/LibWeb/Infra/JSON.cpp
+++ b/Userland/Libraries/LibWeb/Infra/JSON.cpp
@@ -27,7 +27,7 @@ WebIDL::ExceptionOr<JS::Value> parse_json_bytes_to_javascript_value(JS::VM& vm,
 {
     // 1. Let string be the result of running UTF-8 decode on bytes.
     TextCodec::UTF8Decoder decoder;
-    auto string = decoder.to_utf8(bytes);
+    auto string = TRY_OR_THROW_OOM(vm, decoder.to_utf8(bytes));
 
     // 2. Return the result of parsing a JSON string to an Infra value given string.
     return parse_json_string_to_javascript_value(vm, string);
diff --git a/Userland/Libraries/LibWeb/XHR/XMLHttpRequest.cpp b/Userland/Libraries/LibWeb/XHR/XMLHttpRequest.cpp
index 1f8529eb91..e12d38c38e 100644
--- a/Userland/Libraries/LibWeb/XHR/XMLHttpRequest.cpp
+++ b/Userland/Libraries/LibWeb/XHR/XMLHttpRequest.cpp
@@ -224,7 +224,7 @@ DeprecatedString XMLHttpRequest::get_text_response() const
     // If we don't support the decoder yet, let's crash instead of attempting to return something, as the result would be incorrect and create obscure bugs.
     VERIFY(decoder.has_value());
 
-    return TextCodec::convert_input_to_utf8_using_given_decoder_unless_there_is_a_byte_order_mark(*decoder, m_received_bytes);
+    return TextCodec::convert_input_to_utf8_using_given_decoder_unless_there_is_a_byte_order_mark(*decoder, m_received_bytes).release_value_but_fixme_should_propagate_errors().to_deprecated_string();
 }
 
 // https://xhr.spec.whatwg.org/#final-mime-type
diff --git a/Userland/Utilities/js.cpp b/Userland/Utilities/js.cpp
index 855f3b1d27..162741661f 100644
--- a/Userland/Utilities/js.cpp
+++ b/Userland/Utilities/js.cpp
@@ -885,7 +885,7 @@ ErrorOr<int> serenity_main(Main::Arguments arguments)
                     auto decoder = TextCodec::decoder_for("windows-1252"sv);
                     VERIFY(decoder.has_value());
 
-                    auto utf8_source = TextCodec::convert_input_to_utf8_using_given_decoder_unless_there_is_a_byte_order_mark(*decoder, source);
+                    auto utf8_source = TRY(TextCodec::convert_input_to_utf8_using_given_decoder_unless_there_is_a_byte_order_mark(*decoder, source));
                     builder.append(utf8_source);
                 }
             }