diff --git a/Libraries/LibWeb/Compression/CompressionStream.cpp b/Libraries/LibWeb/Compression/CompressionStream.cpp
index c6d12fb809e..d2679dd56cd 100644
--- a/Libraries/LibWeb/Compression/CompressionStream.cpp
+++ b/Libraries/LibWeb/Compression/CompressionStream.cpp
@@ -115,9 +115,8 @@ WebIDL::ExceptionOr<void> CompressionStream::compress_and_enqueue_chunk(JS::Valu
 
     // 2. Let buffer be the result of compressing chunk with cs's format and context.
     auto maybe_buffer = [&]() -> ErrorOr<ByteBuffer> {
-        if (auto buffer = WebIDL::underlying_buffer_source(chunk.as_object()))
-            return compress(buffer->buffer(), Finish::No);
-        return ByteBuffer {};
+        auto chunk_buffer = TRY(WebIDL::get_buffer_source_copy(chunk.as_object()));
+        return compress(move(chunk_buffer), Finish::No);
     }();
     if (maybe_buffer.is_error())
         return WebIDL::SimpleException { WebIDL::SimpleExceptionType::TypeError, MUST(String::formatted("Unable to compress chunk: {}", maybe_buffer.error())) };
diff --git a/Libraries/LibWeb/Compression/DecompressionStream.cpp b/Libraries/LibWeb/Compression/DecompressionStream.cpp
index bc68d40c761..4de816e114e 100644
--- a/Libraries/LibWeb/Compression/DecompressionStream.cpp
+++ b/Libraries/LibWeb/Compression/DecompressionStream.cpp
@@ -117,11 +117,8 @@ WebIDL::ExceptionOr<void> DecompressionStream::decompress_and_enqueue_chunk(JS::
     // 2. Let buffer be the result of decompressing chunk with ds's format and context. If this results in an error,
     //    then throw a TypeError.
     auto maybe_buffer = [&]() -> ErrorOr<ByteBuffer> {
-        auto chunk_buffer = WebIDL::underlying_buffer_source(chunk.as_object());
-        if (!chunk_buffer)
-            return ByteBuffer {};
-
-        TRY(m_input_stream->write_until_depleted(chunk_buffer->buffer()));
+        auto chunk_buffer = TRY(WebIDL::get_buffer_source_copy(chunk.as_object()));
+        TRY(m_input_stream->write_until_depleted(move(chunk_buffer)));
 
         auto decompressed = TRY(ByteBuffer::create_uninitialized(4096));
         auto size = TRY(m_decompressor.visit([&](auto const& decompressor) -> ErrorOr<size_t> {
diff --git a/Tests/LibWeb/Text/expected/wpt-import/compression/compression-large-flush-output.any.txt b/Tests/LibWeb/Text/expected/wpt-import/compression/compression-large-flush-output.any.txt
index a3ab97e1de4..c4769acfffc 100644
--- a/Tests/LibWeb/Text/expected/wpt-import/compression/compression-large-flush-output.any.txt
+++ b/Tests/LibWeb/Text/expected/wpt-import/compression/compression-large-flush-output.any.txt
@@ -2,7 +2,7 @@ Harness status: OK
 
 Found 3 tests
 
-3 Fail
-Fail	deflate compression with large flush output
-Fail	gzip compression with large flush output
-Fail	deflate-raw compression with large flush output
\ No newline at end of file
+3 Pass
+Pass	deflate compression with large flush output
+Pass	gzip compression with large flush output
+Pass	deflate-raw compression with large flush output
\ No newline at end of file