diff --git a/Userland/Libraries/LibWeb/Streams/ReadableStream.cpp b/Userland/Libraries/LibWeb/Streams/ReadableStream.cpp
index c747f6f03f..0707ee7462 100644
--- a/Userland/Libraries/LibWeb/Streams/ReadableStream.cpp
+++ b/Userland/Libraries/LibWeb/Streams/ReadableStream.cpp
@@ -66,7 +66,7 @@ ReadableStream::ReadableStream(JS::Realm& realm)
 ReadableStream::~ReadableStream() = default;
 
 // https://streams.spec.whatwg.org/#rs-locked
-bool ReadableStream::locked()
+bool ReadableStream::locked() const
 {
     // 1. Return ! IsReadableStreamLocked(this).
     return is_readable_stream_locked(*this);
diff --git a/Userland/Libraries/LibWeb/Streams/ReadableStream.h b/Userland/Libraries/LibWeb/Streams/ReadableStream.h
index e9acd15b2f..4ef85ccc4e 100644
--- a/Userland/Libraries/LibWeb/Streams/ReadableStream.h
+++ b/Userland/Libraries/LibWeb/Streams/ReadableStream.h
@@ -34,7 +34,7 @@ public:
 
     virtual ~ReadableStream() override;
 
-    bool locked();
+    bool locked() const;
     WebIDL::ExceptionOr<JS::GCPtr<JS::Object>> cancel(JS::Value view);
     WebIDL::ExceptionOr<ReadableStreamReader> get_reader();