diff --git a/AK/Base64.cpp b/AK/Base64.cpp
index 0093481a67..f60340e1ad 100644
--- a/AK/Base64.cpp
+++ b/AK/Base64.cpp
@@ -100,7 +100,7 @@ ErrorOr<ByteBuffer> decode_base64(StringView input)
     return ByteBuffer::copy(output);
 }
 
-DeprecatedString encode_base64(ReadonlyBytes input)
+ErrorOr<String> encode_base64(ReadonlyBytes input)
 {
     StringBuilder output(calculate_base64_encoded_length(input));
 
@@ -131,13 +131,13 @@ DeprecatedString encode_base64(ReadonlyBytes input)
         char const out2 = is_16bit ? '=' : alphabet[index2];
         char const out3 = is_8bit ? '=' : alphabet[index3];
 
-        output.append(out0);
-        output.append(out1);
-        output.append(out2);
-        output.append(out3);
+        TRY(output.try_append(out0));
+        TRY(output.try_append(out1));
+        TRY(output.try_append(out2));
+        TRY(output.try_append(out3));
     }
 
-    return output.to_deprecated_string();
+    return output.to_string();
 }
 
 }
diff --git a/AK/Base64.h b/AK/Base64.h
index 5635352d00..3bbdf5359b 100644
--- a/AK/Base64.h
+++ b/AK/Base64.h
@@ -7,8 +7,8 @@
 #pragma once
 
 #include <AK/ByteBuffer.h>
-#include <AK/DeprecatedString.h>
 #include <AK/Error.h>
+#include <AK/String.h>
 #include <AK/StringView.h>
 
 namespace AK {
@@ -19,7 +19,7 @@ namespace AK {
 
 [[nodiscard]] ErrorOr<ByteBuffer> decode_base64(StringView);
 
-[[nodiscard]] DeprecatedString encode_base64(ReadonlyBytes);
+[[nodiscard]] ErrorOr<String> encode_base64(ReadonlyBytes);
 }
 
 #if USING_AK_GLOBALLY
diff --git a/Tests/AK/TestBase64.cpp b/Tests/AK/TestBase64.cpp
index 32048b7e61..f6f79b1737 100644
--- a/Tests/AK/TestBase64.cpp
+++ b/Tests/AK/TestBase64.cpp
@@ -42,8 +42,8 @@ TEST_CASE(test_decode_invalid)
 TEST_CASE(test_encode)
 {
     auto encode_equal = [&](StringView input, StringView expected) {
-        auto encoded = encode_base64(input.bytes());
-        EXPECT(encoded == DeprecatedString(expected));
+        auto encoded = MUST(encode_base64(input.bytes()));
+        EXPECT(encoded == expected);
         EXPECT_EQ(expected.length(), calculate_base64_encoded_length(input.bytes()));
     };
 
diff --git a/Userland/Applications/PixelPaint/Image.cpp b/Userland/Applications/PixelPaint/Image.cpp
index e26cf8cdab..ac7e472280 100644
--- a/Userland/Applications/PixelPaint/Image.cpp
+++ b/Userland/Applications/PixelPaint/Image.cpp
@@ -137,9 +137,9 @@ ErrorOr<void> Image::serialize_as_json(JsonObjectSerializer<StringBuilder>& json
             TRY(json_layer.add("opacity_percent"sv, layer.opacity_percent()));
             TRY(json_layer.add("visible"sv, layer.is_visible()));
             TRY(json_layer.add("selected"sv, layer.is_selected()));
-            TRY(json_layer.add("bitmap"sv, encode_base64(TRY(Gfx::PNGWriter::encode(layer.content_bitmap())))));
+            TRY(json_layer.add("bitmap"sv, TRY(encode_base64(TRY(Gfx::PNGWriter::encode(layer.content_bitmap()))))));
             if (layer.is_masked())
-                TRY(json_layer.add("mask"sv, encode_base64(TRY(Gfx::PNGWriter::encode(*layer.mask_bitmap())))));
+                TRY(json_layer.add("mask"sv, TRY(encode_base64(TRY(Gfx::PNGWriter::encode(*layer.mask_bitmap()))))));
             TRY(json_layer.finish());
         }
 
diff --git a/Userland/Libraries/LibCore/Account.cpp b/Userland/Libraries/LibCore/Account.cpp
index 03808e089c..17746d2cac 100644
--- a/Userland/Libraries/LibCore/Account.cpp
+++ b/Userland/Libraries/LibCore/Account.cpp
@@ -34,7 +34,10 @@ static DeprecatedString get_salt()
 
     StringBuilder builder;
     builder.append("$5$"sv);
-    builder.append(encode_base64(ReadonlyBytes(random_data, sizeof(random_data))));
+
+    // FIXME: change to TRY() and make method fallible
+    auto salt_string = MUST(encode_base64({ random_data, sizeof(random_data) }));
+    builder.append(salt_string);
 
     return builder.build();
 }
diff --git a/Userland/Libraries/LibCrypt/crypt.cpp b/Userland/Libraries/LibCrypt/crypt.cpp
index 258f2909f1..fcb378353e 100644
--- a/Userland/Libraries/LibCrypt/crypt.cpp
+++ b/Userland/Libraries/LibCrypt/crypt.cpp
@@ -52,8 +52,13 @@ char* crypt_r(char const* key, char const* salt, struct crypt_data* data)
     sha.update(reinterpret_cast<u8 const*>(salt_value), salt_len);
 
     auto digest = sha.digest();
-    auto string = encode_base64(ReadonlyBytes(digest.immutable_data(), digest.data_length()));
+    auto string_or_error = encode_base64({ digest.immutable_data(), digest.data_length() });
+    if (string_or_error.is_error()) {
+        errno = ENOMEM;
+        return nullptr;
+    }
 
+    auto string = string_or_error.value().bytes_as_string_view();
     fits = string.copy_characters_to_buffer(data->result + header_len + 1, sizeof(data->result) - header_len - 1);
     if (!fits) {
         errno = EINVAL;
diff --git a/Userland/Libraries/LibHTTP/HttpRequest.cpp b/Userland/Libraries/LibHTTP/HttpRequest.cpp
index ab6538e3bc..9ac9255e9f 100644
--- a/Userland/Libraries/LibHTTP/HttpRequest.cpp
+++ b/Userland/Libraries/LibHTTP/HttpRequest.cpp
@@ -242,7 +242,9 @@ Optional<HttpRequest::Header> HttpRequest::get_http_basic_authentication_header(
     builder.append(url.username());
     builder.append(':');
     builder.append(url.password());
-    auto token = encode_base64(builder.to_deprecated_string().bytes());
+
+    // FIXME: change to TRY() and make method fallible
+    auto token = MUST(encode_base64(MUST(builder.to_string()).bytes()));
     builder.clear();
     builder.append("Basic "sv);
     builder.append(token);
diff --git a/Userland/Libraries/LibWeb/Fetch/Fetching/Fetching.cpp b/Userland/Libraries/LibWeb/Fetch/Fetching/Fetching.cpp
index 4845715f5f..ec0846ecb8 100644
--- a/Userland/Libraries/LibWeb/Fetch/Fetching/Fetching.cpp
+++ b/Userland/Libraries/LibWeb/Fetch/Fetching/Fetching.cpp
@@ -1305,7 +1305,8 @@ WebIDL::ExceptionOr<JS::NonnullGCPtr<PendingResponse>> http_network_or_cache_fet
                 //    true, set authorizationValue to httpRequest’s current URL, converted to an `Authorization` value.
                 else if (http_request->current_url().includes_credentials() && is_authentication_fetch == IsAuthenticationFetch::Yes) {
                     auto const& url = http_request->current_url();
-                    authorization_value = encode_base64(DeprecatedString::formatted("{}:{}", url.username(), url.password()).bytes());
+                    auto payload = DeprecatedString::formatted("{}:{}", url.username(), url.password());
+                    authorization_value = TRY_OR_RETURN_OOM(realm, encode_base64(payload.bytes())).to_deprecated_string();
                 }
 
                 // 4. If authorizationValue is non-null, then append (`Authorization`, authorizationValue) to
diff --git a/Userland/Libraries/LibWeb/HTML/HTMLCanvasElement.cpp b/Userland/Libraries/LibWeb/HTML/HTMLCanvasElement.cpp
index faad688c1c..3c4eb53e67 100644
--- a/Userland/Libraries/LibWeb/HTML/HTMLCanvasElement.cpp
+++ b/Userland/Libraries/LibWeb/HTML/HTMLCanvasElement.cpp
@@ -181,7 +181,12 @@ DeprecatedString HTMLCanvasElement::to_data_url(DeprecatedString const& type, [[
         dbgln("Gfx::PNGWriter failed to encode the HTMLCanvasElement: {}", encoded_bitmap_or_error.error());
         return {};
     }
-    return AK::URL::create_with_data(type, encode_base64(encoded_bitmap_or_error.value()), true).to_deprecated_string();
+    auto base64_encoded_or_error = encode_base64(encoded_bitmap_or_error.value());
+    if (base64_encoded_or_error.is_error()) {
+        // FIXME: propagate error
+        return {};
+    }
+    return AK::URL::create_with_data(type, base64_encoded_or_error.release_value().to_deprecated_string(), true).to_deprecated_string();
 }
 
 void HTMLCanvasElement::present()
diff --git a/Userland/Libraries/LibWeb/HTML/Window.cpp b/Userland/Libraries/LibWeb/HTML/Window.cpp
index 5b4147b3d4..52f1707947 100644
--- a/Userland/Libraries/LibWeb/HTML/Window.cpp
+++ b/Userland/Libraries/LibWeb/HTML/Window.cpp
@@ -1423,8 +1423,8 @@ JS_DEFINE_NATIVE_FUNCTION(Window::btoa)
         byte_string.append(code_point);
     }
 
-    auto encoded = encode_base64(byte_string.span());
-    return JS::PrimitiveString::create(vm, move(encoded));
+    auto encoded = MUST(encode_base64(byte_string.span()));
+    return JS::PrimitiveString::create(vm, encoded.to_deprecated_string());
 }
 
 // https://html.spec.whatwg.org/multipage/interaction.html#dom-window-focus
diff --git a/Userland/Libraries/LibWeb/HTML/WorkerGlobalScope.cpp b/Userland/Libraries/LibWeb/HTML/WorkerGlobalScope.cpp
index bad102430e..09bf7004c3 100644
--- a/Userland/Libraries/LibWeb/HTML/WorkerGlobalScope.cpp
+++ b/Userland/Libraries/LibWeb/HTML/WorkerGlobalScope.cpp
@@ -137,7 +137,7 @@ WebIDL::ExceptionOr<DeprecatedString> WorkerGlobalScope::btoa(DeprecatedString c
 
     // Otherwise, the user agent must convert data to a byte sequence whose nth byte is the eight-bit representation of the nth code point of data,
     // and then must apply forgiving-base64 encode to that byte sequence and return the result.
-    return encode_base64(byte_string.span());
+    return TRY_OR_RETURN_OOM(realm(), encode_base64(byte_string.span())).to_deprecated_string();
 }
 
 // https://html.spec.whatwg.org/multipage/webappapis.html#dom-atob
diff --git a/Userland/Libraries/LibWebSocket/WebSocket.cpp b/Userland/Libraries/LibWebSocket/WebSocket.cpp
index 78147eb608..f3072c7aa7 100644
--- a/Userland/Libraries/LibWebSocket/WebSocket.cpp
+++ b/Userland/Libraries/LibWebSocket/WebSocket.cpp
@@ -180,7 +180,8 @@ void WebSocket::send_client_handshake()
     // 7. 16-byte nonce encoded as Base64
     u8 nonce_data[16];
     fill_with_random(nonce_data, 16);
-    m_websocket_key = encode_base64(ReadonlyBytes(nonce_data, 16));
+    // FIXME: change to TRY() and make method fallible
+    m_websocket_key = MUST(encode_base64({ nonce_data, 16 })).to_deprecated_string();
     builder.appendff("Sec-WebSocket-Key: {}\r\n", m_websocket_key);
 
     // 8. Origin (optional field)
@@ -322,7 +323,8 @@ void WebSocket::read_server_handshake()
             hash.initialize(Crypto::Hash::HashKind::SHA1);
             hash.update(expected_content);
             auto expected_sha1 = hash.digest();
-            auto expected_sha1_string = encode_base64(ReadonlyBytes(expected_sha1.immutable_data(), expected_sha1.data_length()));
+            // FIXME: change to TRY() and make method fallible
+            auto expected_sha1_string = MUST(encode_base64({ expected_sha1.immutable_data(), expected_sha1.data_length() }));
             if (!parts[1].trim_whitespace().equals_ignoring_case(expected_sha1_string)) {
                 dbgln("WebSocket: Server HTTP Handshake Header |Sec-Websocket-Accept| should be '{}', got '{}'. Failing connection.", expected_sha1_string, parts[1]);
                 fatal_error(WebSocket::Error::ConnectionUpgradeFailed);
diff --git a/Userland/Services/WebServer/Client.cpp b/Userland/Services/WebServer/Client.cpp
index 2571f88684..84728f3c2c 100644
--- a/Userland/Services/WebServer/Client.cpp
+++ b/Userland/Services/WebServer/Client.cpp
@@ -238,7 +238,8 @@ static DeprecatedString folder_image_data()
     static DeprecatedString cache;
     if (cache.is_empty()) {
         auto file = Core::MappedFile::map("/res/icons/16x16/filetype-folder.png"sv).release_value_but_fixme_should_propagate_errors();
-        cache = encode_base64(file->bytes());
+        // FIXME: change to TRY() and make method fallible
+        cache = MUST(encode_base64(file->bytes())).to_deprecated_string();
     }
     return cache;
 }
@@ -248,7 +249,8 @@ static DeprecatedString file_image_data()
     static DeprecatedString cache;
     if (cache.is_empty()) {
         auto file = Core::MappedFile::map("/res/icons/16x16/filetype-unknown.png"sv).release_value_but_fixme_should_propagate_errors();
-        cache = encode_base64(file->bytes());
+        // FIXME: change to TRY() and make method fallible
+        cache = MUST(encode_base64(file->bytes())).to_deprecated_string();
     }
     return cache;
 }
diff --git a/Userland/Utilities/useradd.cpp b/Userland/Utilities/useradd.cpp
index 146d2c598f..f84e4c19ea 100644
--- a/Userland/Utilities/useradd.cpp
+++ b/Userland/Utilities/useradd.cpp
@@ -134,18 +134,18 @@ ErrorOr<int> serenity_main(Main::Arguments arguments)
         }
     }
 
-    auto get_salt = []() {
+    auto get_salt = []() -> ErrorOr<DeprecatedString> {
         char random_data[12];
         fill_with_random(random_data, sizeof(random_data));
 
         StringBuilder builder;
         builder.append("$5$"sv);
-        builder.append(encode_base64(ReadonlyBytes(random_data, sizeof(random_data))));
+        builder.append(TRY(encode_base64({ random_data, sizeof(random_data) })));
 
         return builder.build();
     };
 
-    char* hash = crypt(password.characters(), get_salt().characters());
+    char* hash = crypt(password.characters(), TRY(get_salt()).characters());
 
     struct passwd p;
     p.pw_name = const_cast<char*>(username.characters());