diff --git a/spec/asynciterable/inference-spec.ts b/spec/asynciterable/inference-spec.ts
index deddd551..77726de6 100644
--- a/spec/asynciterable/inference-spec.ts
+++ b/spec/asynciterable/inference-spec.ts
@@ -32,11 +32,11 @@ describe('AsyncIterable type inference', () => {
 
   if (TEST_DOM_STREAMS) {
     test('#pipeThrough type inference is correct with transform stream', () => {
-      const source = of(0, 1, 2).pipeThrough(new TransformStream());
+      const source = of(0, 1, 2).pipeThrough(new TransformStream<number, number>());
       expect(source).toEqualStream([0, 1, 2]);
     });
     test('#pipeThrough type inference is correct with transform stream and pipe options', () => {
-      const source = of(0, 1, 2).pipeThrough(new TransformStream(), {
+      const source = of(0, 1, 2).pipeThrough(new TransformStream<number, number>(), {
         preventClose: false,
       });
       expect(source).toEqualStream([0, 1, 2]);
diff --git a/spec/iterable/inference-spec.ts b/spec/iterable/inference-spec.ts
index 948a224c..a2d2d269 100644
--- a/spec/iterable/inference-spec.ts
+++ b/spec/iterable/inference-spec.ts
@@ -33,11 +33,11 @@ describe('Iterable type inference', () => {
 
   if (TEST_DOM_STREAMS) {
     test('#pipeThrough type inference is correct with writable stream', () => {
-      const source = of(0, 1, 2).pipeThrough(new TransformStream());
+      const source = of(0, 1, 2).pipeThrough(new TransformStream<number, number>());
       expect(source).toEqualStream([0, 1, 2]);
     });
     test('#pipeThrough type inference is correct with writable stream and pipe options', () => {
-      const source = of(0, 1, 2).pipeThrough(new TransformStream(), {
+      const source = of(0, 1, 2).pipeThrough(new TransformStream<number, number>(), {
         preventClose: false,
       });
       expect(source).toEqualStream([0, 1, 2]);
diff --git a/src/asynciterable/todomstream.ts b/src/asynciterable/todomstream.ts
index aeb8e475..cb052851 100644
--- a/src/asynciterable/todomstream.ts
+++ b/src/asynciterable/todomstream.ts
@@ -267,6 +267,6 @@ declare module '../asynciterable/asynciterablex' {
     pipeThrough<R extends ReadableStream<any>>(
       duplex: { writable: WritableStream<T>; readable: R },
       options?: StreamPipeOptions
-    ): ReadableStream<T>;
+    ): R;
   }
 }
diff --git a/src/iterable/todomstream.ts b/src/iterable/todomstream.ts
index 0c9c4482..000d24e6 100644
--- a/src/iterable/todomstream.ts
+++ b/src/iterable/todomstream.ts
@@ -85,6 +85,6 @@ declare module '../iterable/iterablex' {
     pipeThrough<R extends ReadableStream<any>>(
       duplex: { writable: WritableStream<T>; readable: R },
       options?: StreamPipeOptions
-    ): ReadableStream<T>;
+    ): R;
   }
 }