diff --git a/Userland/Libraries/LibTextCodec/Decoder.cpp b/Userland/Libraries/LibTextCodec/Decoder.cpp
index c6cd6445c52..e1f6c57f11a 100644
--- a/Userland/Libraries/LibTextCodec/Decoder.cpp
+++ b/Userland/Libraries/LibTextCodec/Decoder.cpp
@@ -531,10 +531,15 @@ StringView get_output_encoding(StringView encoding)
     return encoding;
 }
 
-bool Decoder::validate(StringView)
+bool Decoder::validate(StringView input)
 {
-    // By-default we assume that any input sequence is valid, character encodings that do not accept all inputs may override this
-    return true;
+    auto result = this->process(input, [](auto code_point) -> ErrorOr<void> {
+        if (code_point == replacement_code_point)
+            return Error::from_errno(EINVAL);
+        return {};
+    });
+
+    return !result.is_error();
 }
 
 ErrorOr<String> Decoder::to_utf8(StringView input)
diff --git a/Userland/Libraries/LibTextCodec/Decoder.h b/Userland/Libraries/LibTextCodec/Decoder.h
index 26f161bbac6..0c8d23b0d39 100644
--- a/Userland/Libraries/LibTextCodec/Decoder.h
+++ b/Userland/Libraries/LibTextCodec/Decoder.h
@@ -62,31 +62,37 @@ private:
 class Latin1Decoder final : public Decoder {
 public:
     virtual ErrorOr<void> process(StringView, Function<ErrorOr<void>(u32)> on_code_point) override;
+    virtual bool validate(StringView) override { return true; }
 };
 
 class Latin2Decoder final : public Decoder {
 public:
     virtual ErrorOr<void> process(StringView, Function<ErrorOr<void>(u32)> on_code_point) override;
+    virtual bool validate(StringView) override { return true; }
 };
 
 class Latin9Decoder final : public Decoder {
 public:
     virtual ErrorOr<void> process(StringView, Function<ErrorOr<void>(u32)> on_code_point) override;
+    virtual bool validate(StringView) override { return true; }
 };
 
 class PDFDocEncodingDecoder final : public Decoder {
 public:
     virtual ErrorOr<void> process(StringView, Function<ErrorOr<void>(u32)> on_code_point) override;
+    virtual bool validate(StringView) override { return true; }
 };
 
 class TurkishDecoder final : public Decoder {
 public:
     virtual ErrorOr<void> process(StringView, Function<ErrorOr<void>(u32)> on_code_point) override;
+    virtual bool validate(StringView) override { return true; }
 };
 
 class XUserDefinedDecoder final : public Decoder {
 public:
     virtual ErrorOr<void> process(StringView, Function<ErrorOr<void>(u32)> on_code_point) override;
+    virtual bool validate(StringView) override { return true; }
 };
 
 Optional<Decoder&> decoder_for(StringView encoding);