diff --git a/Userland/Libraries/LibTextCodec/Decoder.cpp b/Userland/Libraries/LibTextCodec/Decoder.cpp
index 37a28d5999..bebdb004a3 100644
--- a/Userland/Libraries/LibTextCodec/Decoder.cpp
+++ b/Userland/Libraries/LibTextCodec/Decoder.cpp
@@ -64,24 +64,26 @@ CyrillicDecoder& cyrillic_decoder()
 Decoder* decoder_for(const String& a_encoding)
 {
     auto encoding = get_standardized_encoding(a_encoding);
-    if (encoding.equals_ignoring_case("windows-1252"))
-        return &latin1_decoder();
-    if (encoding.equals_ignoring_case("utf-8"))
-        return &utf8_decoder();
-    if (encoding.equals_ignoring_case("utf-16be"))
-        return &utf16be_decoder();
-    if (encoding.equals_ignoring_case("iso-8859-2"))
-        return &latin2_decoder();
-    if (encoding.equals_ignoring_case("windows-1255"))
-        return &hebrew_decoder();
-    if (encoding.equals_ignoring_case("windows-1251"))
-        return &cyrillic_decoder();
+    if (encoding.has_value()) {
+        if (encoding.value().equals_ignoring_case("windows-1252"))
+            return &latin1_decoder();
+        if (encoding.value().equals_ignoring_case("utf-8"))
+            return &utf8_decoder();
+        if (encoding.value().equals_ignoring_case("utf-16be"))
+            return &utf16be_decoder();
+        if (encoding.value().equals_ignoring_case("iso-8859-2"))
+            return &latin2_decoder();
+        if (encoding.value().equals_ignoring_case("windows-1255"))
+            return &hebrew_decoder();
+        if (encoding.value().equals_ignoring_case("windows-1251"))
+            return &cyrillic_decoder();
+    }
     dbgln("TextCodec: No decoder implemented for encoding '{}'", a_encoding);
     return nullptr;
 }
 
 // https://encoding.spec.whatwg.org/#concept-encoding-get
-String get_standardized_encoding(const String& encoding)
+Optional<String> get_standardized_encoding(const String& encoding)
 {
     String trimmed_lowercase_encoding = encoding.trim_whitespace().to_lowercase();
 
@@ -172,7 +174,8 @@ String get_standardized_encoding(const String& encoding)
 
 bool is_standardized_encoding(const String& encoding)
 {
-    return encoding.equals_ignoring_case(get_standardized_encoding(encoding));
+    auto standardized_encoding = get_standardized_encoding(encoding);
+    return standardized_encoding.has_value() && encoding.equals_ignoring_case(standardized_encoding.value());
 }
 
 String UTF8Decoder::to_utf8(const StringView& input)
diff --git a/Userland/Libraries/LibTextCodec/Decoder.h b/Userland/Libraries/LibTextCodec/Decoder.h
index 6ea4147b7e..585f05ff0d 100644
--- a/Userland/Libraries/LibTextCodec/Decoder.h
+++ b/Userland/Libraries/LibTextCodec/Decoder.h
@@ -49,7 +49,7 @@ public:
 };
 
 Decoder* decoder_for(const String& encoding);
-String get_standardized_encoding(const String& encoding);
+Optional<String> get_standardized_encoding(const String& encoding);
 bool is_standardized_encoding(const String& encoding);
 
 }
diff --git a/Userland/Libraries/LibWeb/HTML/Parser/HTMLDocumentParser.cpp b/Userland/Libraries/LibWeb/HTML/Parser/HTMLDocumentParser.cpp
index 635e07ea6d..e0c5efc4b2 100644
--- a/Userland/Libraries/LibWeb/HTML/Parser/HTMLDocumentParser.cpp
+++ b/Userland/Libraries/LibWeb/HTML/Parser/HTMLDocumentParser.cpp
@@ -104,7 +104,9 @@ HTMLDocumentParser::HTMLDocumentParser(DOM::Document& document, const StringView
     , m_document(document)
 {
     m_document->set_should_invalidate_styles_on_attribute_changes(false);
-    m_document->set_encoding(TextCodec::get_standardized_encoding(encoding));
+    auto standardized_encoding = TextCodec::get_standardized_encoding(encoding);
+    VERIFY(standardized_encoding.has_value());
+    m_document->set_encoding(standardized_encoding.value());
 }
 
 HTMLDocumentParser::~HTMLDocumentParser()