diff --git a/src/browser/streams/ReadableStream.zig b/src/browser/streams/ReadableStream.zig
index a25fd635..a33459d6 100644
--- a/src/browser/streams/ReadableStream.zig
+++ b/src/browser/streams/ReadableStream.zig
@@ -75,7 +75,15 @@ pub fn constructor(underlying: ?UnderlyingSource, strategy: ?QueueingStrategy, p
     return stream;
 }
 
-pub fn _cancel(self: *const ReadableStream, page: *Page) Env.Promise {
+pub fn get_locked(self: *const ReadableStream) bool {
+    return self.locked;
+}
+
+pub fn _cancel(self: *const ReadableStream, page: *Page) !Env.Promise {
+    if (self.locked) {
+        return error.TypeError;
+    }
+
     const resolver = Env.PromiseResolver{
         .js_context = page.main_context,
         .resolver = self.cancel_resolver.castToPromiseResolver(),
@@ -84,21 +92,28 @@ pub fn _cancel(self: *const ReadableStream, page: *Page) Env.Promise {
     return resolver.promise();
 }
 
-pub fn get_locked(self: *const ReadableStream) bool {
-    return self.locked;
-}
-
 const GetReaderOptions = struct {
+    // Mode must equal 'byob' or be undefined. RangeError otherwise.
     mode: ?[]const u8 = null,
 };
 
-pub fn _getReader(self: *ReadableStream, _options: ?GetReaderOptions, page: *Page) ReadableStreamDefaultReader {
+pub fn _getReader(self: *ReadableStream, _options: ?GetReaderOptions, page: *Page) !ReadableStreamDefaultReader {
+    if (self.locked) {
+        return error.TypeError;
+    }
+
     const options = _options orelse GetReaderOptions{};
     _ = options;
 
     return ReadableStreamDefaultReader.constructor(self, page);
 }
 
+// TODO: pipeThrough (requires TransformStream)
+
+// TODO: pipeTo (requires WritableStream)
+
+// TODO: tee
+
 const testing = @import("../../testing.zig");
 test "streams: ReadableStream" {
     var runner = try testing.jsRunner(testing.tracking_allocator, .{ .url = "https://lightpanda.io" });
diff --git a/src/browser/streams/ReadableStreamDefaultController.zig b/src/browser/streams/ReadableStreamDefaultController.zig
index 4cd10c7a..ed1ca9a9 100644
--- a/src/browser/streams/ReadableStreamDefaultController.zig
+++ b/src/browser/streams/ReadableStreamDefaultController.zig
@@ -54,5 +54,4 @@ pub fn _enqueue(self: *ReadableStreamDefaultController, chunk: []const u8, page:
 
 pub fn _error(self: *ReadableStreamDefaultController, err: Env.JsObject) void {
     self.stream.state = .{ .errored = err };
-    // set to error.
 }
diff --git a/src/browser/streams/ReadableStreamDefaultReader.zig b/src/browser/streams/ReadableStreamDefaultReader.zig
index 307dd75e..1646a855 100644
--- a/src/browser/streams/ReadableStreamDefaultReader.zig
+++ b/src/browser/streams/ReadableStreamDefaultReader.zig
@@ -47,8 +47,8 @@ pub fn get_closed(self: *const ReadableStreamDefaultReader) Env.Promise {
     return self.closed_resolver.promise();
 }
 
-pub fn _cancel(self: *ReadableStreamDefaultReader, page: *Page) Env.Promise {
-    return self.stream._cancel(page);
+pub fn _cancel(self: *ReadableStreamDefaultReader, page: *Page) !Env.Promise {
+    return try self.stream._cancel(page);
 }
 
 pub const ReadableStreamReadResult = struct {