diff --git a/Userland/Libraries/LibWeb/Streams/ReadableByteStreamController.h b/Userland/Libraries/LibWeb/Streams/ReadableByteStreamController.h
index f4e3c79804..b8f09f3442 100644
--- a/Userland/Libraries/LibWeb/Streams/ReadableByteStreamController.h
+++ b/Userland/Libraries/LibWeb/Streams/ReadableByteStreamController.h
@@ -27,23 +27,23 @@ struct PullIntoDescriptor {
 
     // https://streams.spec.whatwg.org/#pull-into-descriptor-buffer-byte-length
     // A positive integer representing the initial byte length of buffer
-    u32 buffer_byte_length;
+    u64 buffer_byte_length;
 
     // https://streams.spec.whatwg.org/#pull-into-descriptor-byte-offset
     // A nonnegative integer byte offset into the buffer where the underlying byte source will start writing
-    u32 byte_offset;
+    u64 byte_offset;
 
     // https://streams.spec.whatwg.org/#pull-into-descriptor-byte-length
     // A positive integer number of bytes which can be written into the buffer
-    u32 byte_length;
+    u64 byte_length;
 
     // https://streams.spec.whatwg.org/#pull-into-descriptor-bytes-filled
     // A nonnegative integer number of bytes that have been written into the buffer so far
-    u32 bytes_filled;
+    u64 bytes_filled;
 
     // https://streams.spec.whatwg.org/#pull-into-descriptor-element-size
     // A positive integer representing the number of bytes that can be written into the buffer at a time, using views of the type described by the view constructor
-    u32 element_size;
+    u64 element_size;
 
     // https://streams.spec.whatwg.org/#pull-into-descriptor-view-constructor
     // A typed array constructor or %DataView%, which will be used for constructing a view with which to write into the buffer
@@ -62,11 +62,11 @@ struct ReadableByteStreamQueueEntry {
 
     // https://streams.spec.whatwg.org/#readable-byte-stream-queue-entry-byte-offset
     // A nonnegative integer number giving the byte offset derived from the view originally supplied by the underlying byte source
-    u32 byte_offset;
+    u64 byte_offset;
 
     // https://streams.spec.whatwg.org/#readable-byte-stream-queue-entry-byte-length
     // A nonnegative integer number giving the byte length derived from the view originally supplied by the underlying byte source
-    u32 byte_length;
+    u64 byte_length;
 };
 
 // https://streams.spec.whatwg.org/#readablebytestreamcontroller
@@ -83,8 +83,8 @@ public:
     WebIDL::ExceptionOr<void> close();
     void error(JS::Value error);
 
-    Optional<u32> const& auto_allocate_chunk_size() { return m_auto_allocate_chunk_size; }
-    void set_auto_allocate_chunk_size(Optional<u32> value) { m_auto_allocate_chunk_size = value; }
+    Optional<u64> const& auto_allocate_chunk_size() { return m_auto_allocate_chunk_size; }
+    void set_auto_allocate_chunk_size(Optional<u64> value) { m_auto_allocate_chunk_size = value; }
 
     auto& cancel_algorithm() { return m_cancel_algorithm; }
     void set_cancel_algorithm(Optional<CancelAlgorithm> value) { m_cancel_algorithm = move(value); }
@@ -129,7 +129,7 @@ private:
 
     // https://streams.spec.whatwg.org/#readablebytestreamcontroller-autoallocatechunksize
     // A positive integer, when the automatic buffer allocation feature is enabled. In that case, this value specifies the size of buffer to allocate. It is undefined otherwise.
-    Optional<u32> m_auto_allocate_chunk_size;
+    Optional<u64> m_auto_allocate_chunk_size;
 
     // https://streams.spec.whatwg.org/#readablebytestreamcontroller-byobrequest
     // A ReadableStreamBYOBRequest instance representing the current BYOB pull request, or null if there are no pending requests
diff --git a/Userland/Libraries/LibWeb/Streams/UnderlyingSource.cpp b/Userland/Libraries/LibWeb/Streams/UnderlyingSource.cpp
index 8062be06c0..27caa53435 100644
--- a/Userland/Libraries/LibWeb/Streams/UnderlyingSource.cpp
+++ b/Userland/Libraries/LibWeb/Streams/UnderlyingSource.cpp
@@ -36,7 +36,7 @@ JS::ThrowCompletionOr<UnderlyingSource> UnderlyingSource::from_value(JS::VM& vm,
     }
 
     if (TRY(object.has_property("autoAllocateChunkSize")))
-        underlying_source.auto_allocate_chunk_size = TRY(TRY(object.get("autoAllocateChunkSize")).to_bigint_int64(vm));
+        underlying_source.auto_allocate_chunk_size = TRY(TRY(object.get("autoAllocateChunkSize")).to_bigint_uint64(vm));
 
     return underlying_source;
 }
diff --git a/Userland/Libraries/LibWeb/Streams/UnderlyingSource.h b/Userland/Libraries/LibWeb/Streams/UnderlyingSource.h
index 08daab383a..2e282867ba 100644
--- a/Userland/Libraries/LibWeb/Streams/UnderlyingSource.h
+++ b/Userland/Libraries/LibWeb/Streams/UnderlyingSource.h
@@ -23,7 +23,7 @@ struct UnderlyingSource {
     JS::Handle<WebIDL::CallbackType> pull;
     JS::Handle<WebIDL::CallbackType> cancel;
     Optional<ReadableStreamType> type;
-    Optional<i64> auto_allocate_chunk_size;
+    Optional<u64> auto_allocate_chunk_size;
 
     static JS::ThrowCompletionOr<UnderlyingSource> from_value(JS::VM&, JS::Value);
 };