diff --git a/deno2/deno.cc b/deno2/deno.cc
index e158a0e9a37c96..c21dc43c027dbf 100644
--- a/deno2/deno.cc
+++ b/deno2/deno.cc
@@ -144,17 +144,12 @@ void Pub(const v8::FunctionCallbackInfo<v8::Value>& args) {
 
   auto retbuf = d->cb(d, deno_buf{buf, buflen});
   if (retbuf.data) {
-    auto ab = v8::ArrayBuffer::New(d->isolate, retbuf.data, retbuf.len,
-                                   v8::ArrayBufferCreationMode::kInternalized);
-    /*
-    // I'm slightly worried the above v8::ArrayBuffer construction leaks memory
-    // the following might be a safer way to do it.
+    // TODO(ry) Support zero-copy.
     auto ab = v8::ArrayBuffer::New(d->isolate, retbuf.len);
-    auto contents = ab->GetContents();
-    memcpy(contents.Data(), retbuf.data, retbuf.len);
-    free(retbuf.data);
-    */
+    memcpy(ab->GetContents().Data(), retbuf.data, retbuf.len);
     args.GetReturnValue().Set(handle_scope.Escape(ab));
+  } else {
+    args.GetReturnValue().Set(v8::Null(d->isolate));
   }
 }
 
@@ -207,7 +202,8 @@ v8::StartupData MakeSnapshot(v8::StartupData* prev_natives_blob,
     v8::Context::Scope context_scope(context);
 
     auto global = context->Global();
-
+    // TODO(ry) Add a global namespace object "deno" and move print, sub, and
+    // pub inside that object.
     auto print_tmpl = v8::FunctionTemplate::New(isolate, Print);
     auto print_val = print_tmpl->GetFunction(context).ToLocalChecked();
     CHECK(
diff --git a/deno2/js/mock_runtime.js b/deno2/js/mock_runtime.js
index b3ec7f03487206..97688a08d9dd0c 100644
--- a/deno2/js/mock_runtime.js
+++ b/deno2/js/mock_runtime.js
@@ -1,18 +1,42 @@
 // A simple runtime that doesn't involve typescript or protobufs to test
 // libdeno.
 const window = eval("this");
-window['foo'] = () => {
+window["foo"] = () => {
   deno_print("Hello world from foo");
   return "foo";
-}
+};
 
 function assert(cond) {
   if (!cond) throw Error("mock_runtime.js assert failed");
 }
 
 function subabc() {
-  deno_sub((msg) => {
+  deno_sub(msg => {
     assert(msg instanceof ArrayBuffer);
     assert(msg.byteLength === 3);
   });
 }
+
+function typedArrayToArrayBuffer(ta) {
+  return ta.buffer.slice(ta.byteOffset, ta.byteOffset + ta.byteLength);
+}
+
+function pubReturnEmpty() {
+  const ui8 = new Uint8Array("abc".split("").map(c => c.charCodeAt(0)));
+  const ab = typedArrayToArrayBuffer(ui8);
+  let r = deno_pub(ab);
+  assert(r == null);
+  r = deno_pub(ab);
+  assert(r == null);
+}
+
+function pubReturnBar() {
+  const ui8 = new Uint8Array("abc".split("").map(c => c.charCodeAt(0)));
+  const ab = typedArrayToArrayBuffer(ui8);
+  const r = deno_pub(ab);
+  assert(r instanceof ArrayBuffer);
+  assert(r.byteLength === 3);
+  const rui8 = new Uint8Array(r);
+  const rstr = String.fromCharCode(...rui8);
+  assert(rstr === "bar");
+}
diff --git a/deno2/mock_runtime_test.cc b/deno2/mock_runtime_test.cc
index 1d8a6545747af0..6f6688f48e96ab 100644
--- a/deno2/mock_runtime_test.cc
+++ b/deno2/mock_runtime_test.cc
@@ -49,6 +49,40 @@ TEST(MockRuntimeTest, PubNoCallback) {
   deno_dispose(d);
 }
 
+TEST(MockRuntimeTest, SubReturnEmpty) {
+  static int count = 0;
+  Deno* d = deno_new(NULL, [](Deno* _, deno_buf buf) {
+    count++;
+    EXPECT_EQ(static_cast<size_t>(3), buf.len);
+    // TODO(ry) buf.data should just be a char*.
+    char* data = reinterpret_cast<char*>(buf.data);
+    EXPECT_EQ(data[0], 'a');
+    EXPECT_EQ(data[1], 'b');
+    EXPECT_EQ(data[2], 'c');
+    return deno_buf{nullptr, 0};
+  });
+  EXPECT_TRUE(deno_load(d, "a.js", "pubReturnEmpty()"));
+  EXPECT_EQ(count, 2);
+  deno_dispose(d);
+}
+
+TEST(MockRuntimeTest, SubReturnBar) {
+  static int count = 0;
+  Deno* d = deno_new(NULL, [](Deno* _, deno_buf buf) {
+    count++;
+    EXPECT_EQ(static_cast<size_t>(3), buf.len);
+    // TODO(ry) buf.data should just be a char*.
+    char* data = reinterpret_cast<char*>(buf.data);
+    EXPECT_EQ(data[0], 'a');
+    EXPECT_EQ(data[1], 'b');
+    EXPECT_EQ(data[2], 'c');
+    return strbuf("bar");
+  });
+  EXPECT_TRUE(deno_load(d, "a.js", "pubReturnBar()"));
+  EXPECT_EQ(count, 1);
+  deno_dispose(d);
+}
+
 int main(int argc, char** argv) {
   testing::InitGoogleTest(&argc, argv);
   deno_init();