diff --git a/src/stream.ts b/src/stream.ts
index 5f7dd52..8f3bfd8 100644
--- a/src/stream.ts
+++ b/src/stream.ts
@@ -276,6 +276,11 @@ export function changes<A>(
   b: Behavior<A>,
   comparator: (v: A, u: A) => boolean = (v, u) => v === u
 ): Stream<A> {
+  if (b.state === State.Pull) {
+    throw new Error(
+      "You invoked changes on a pull behavior which is not supported."
+    );
+  }
   return new ChangesStream(b, comparator);
 }
 
diff --git a/test/stream.ts b/test/stream.ts
index df00507..f525e13 100644
--- a/test/stream.ts
+++ b/test/stream.ts
@@ -468,18 +468,11 @@ describe("stream", () => {
         [{ a: 1, b: 0 }]
       ]);
     });
-    /*
-    it("gives changes from pulling behavior", () => {
-      let x = 0;
-      const b = fromFunction(() => x);
-      const s = changes(b);
-      const cb = spy();
-      observe
-      x = 1;
-      x = 2;
-      x = 3;
-      assert.deepEqual(cb.args, [[1], [2], [3]]);
+    it("throws on pull behavior", () => {
+      const b = fromFunction(() => "hello");
+      assert.throws(() => {
+        H.changes(b);
+      }, /.*pull behavior.*/);
     });
-    */
   });
 });