diff --git a/deno2/deno.cc b/deno2/deno.cc
index 7bca590a70..4fa5b21018 100644
--- a/deno2/deno.cc
+++ b/deno2/deno.cc
@@ -274,9 +274,10 @@ bool deno_load(Deno* d, const char* name_s, const char* source_s) {
   return deno::Load(context, name_s, source_s);
 }
 
-// Called from golang. Must route message to javascript lang.
-// non-zero return value indicates error. check deno_last_exception().
-int deno_send(Deno* d, deno_buf buf) {
+// Routes message to the javascript callback set with deno_recv().
+// False return value indicates error. Check deno_last_exception() for exception
+// text.
+bool deno_send(Deno* d, deno_buf buf) {
   v8::Locker locker(d->isolate);
   v8::Isolate::Scope isolate_scope(d->isolate);
   v8::HandleScope handle_scope(d->isolate);
@@ -289,8 +290,8 @@ int deno_send(Deno* d, deno_buf buf) {
   v8::Local<v8::Function> recv =
       v8::Local<v8::Function>::New(d->isolate, d->recv);
   if (recv.IsEmpty()) {
-    d->last_exception = "V8Deno2.recv has not been called.";
-    return 1;
+    d->last_exception = "deno_recv has not been called.";
+    return false;
   }
 
   v8::Local<v8::Value> args[1];
@@ -303,10 +304,10 @@ int deno_send(Deno* d, deno_buf buf) {
 
   if (try_catch.HasCaught()) {
     deno::HandleException(context, try_catch.Exception());
-    return 2;
+    return false;
   }
 
-  return 0;
+  return true;
 }
 
 void deno_dispose(Deno* d) {
diff --git a/deno2/include/deno.h b/deno2/include/deno.h
index 1a42ec2b1e..f67a7cf51d 100644
--- a/deno2/include/deno.h
+++ b/deno2/include/deno.h
@@ -31,8 +31,9 @@ Deno* deno_new(void* data, deno_recv_cb cb);
 // Get error text with deno_last_exception().
 bool deno_load(Deno* d, const char* name_s, const char* source_s);
 
-// Returns nonzero on error.
-int deno_send(Deno* d, deno_buf buf);
+// Returns false on error.
+// Get error text with deno_last_exception().
+bool deno_send(Deno* d, deno_buf buf);
 
 const char* deno_last_exception(Deno* d);
 
diff --git a/deno2/js/mock_runtime.js b/deno2/js/mock_runtime.js
index a91546f859..cd97666851 100644
--- a/deno2/js/mock_runtime.js
+++ b/deno2/js/mock_runtime.js
@@ -7,3 +7,13 @@ window['foo'] = () => {
   return "foo";
 }
 
+function assert(cond) {
+  if (!cond) throw Error("assert failed");
+}
+
+function recvabc() {
+  deno_recv((msg) => {
+    assert(msg instanceof ArrayBuffer);
+    assert(msg.byteLength === 3);
+  });
+}
diff --git a/deno2/mock_runtime_test.cc b/deno2/mock_runtime_test.cc
index 951710fb92..00651f68ee 100644
--- a/deno2/mock_runtime_test.cc
+++ b/deno2/mock_runtime_test.cc
@@ -19,6 +19,30 @@ TEST(MockRuntimeTest, ErrorsCorrectly) {
   EXPECT_FALSE(deno_load(d, "a.js", "throw Error()"));
 }
 
+deno_buf strbuf(const char* str) {
+  void* d = reinterpret_cast<void*>(const_cast<char*>(str));
+  return deno_buf{d, strlen(str)};
+}
+
+TEST(MockRuntimeTest, SendSuccess) {
+  Deno* d = deno_new(NULL, NULL);
+  EXPECT_TRUE(deno_load(d, "a.js", "recvabc();"));
+  EXPECT_TRUE(deno_send(d, strbuf("abc")));
+}
+
+TEST(MockRuntimeTest, SendByteLength) {
+  Deno* d = deno_new(NULL, NULL);
+  EXPECT_TRUE(deno_load(d, "a.js", "recvabc();"));
+  // We send the wrong sized message, it should throw.
+  EXPECT_FALSE(deno_send(d, strbuf("abcd")));
+}
+
+TEST(MockRuntimeTest, SendNoCallback) {
+  Deno* d = deno_new(NULL, NULL);
+  // We didn't call deno_recv(), sending should fail.
+  EXPECT_FALSE(deno_send(d, strbuf("abc")));
+}
+
 int main(int argc, char** argv) {
   testing::InitGoogleTest(&argc, argv);
   deno_init();