diff --git a/libdeno/api.cc b/libdeno/api.cc
index af3c4b2156..2c72b1265c 100644
--- a/libdeno/api.cc
+++ b/libdeno/api.cc
@@ -112,8 +112,8 @@ const char* deno_last_exception(Deno* d_) {
   }
 }
 
-int deno_execute(Deno* d_, void* user_data, const char* js_filename,
-                 const char* js_source) {
+void deno_execute(Deno* d_, void* user_data, const char* js_filename,
+                  const char* js_source) {
   auto* d = unwrap(d_);
   deno::UserDataScope user_data_scope(d, user_data);
   auto* isolate = d->isolate_;
@@ -122,17 +122,17 @@ int deno_execute(Deno* d_, void* user_data, const char* js_filename,
   v8::HandleScope handle_scope(isolate);
   auto context = d->context_.Get(d->isolate_);
   CHECK(!context.IsEmpty());
-  return deno::Execute(context, js_filename, js_source) ? 1 : 0;
+  deno::Execute(context, js_filename, js_source);
 }
 
-int deno_respond(Deno* d_, void* user_data, int32_t req_id, deno_buf buf) {
+void deno_respond(Deno* d_, void* user_data, int32_t req_id, deno_buf buf) {
   auto* d = unwrap(d_);
   if (d->current_args_ != nullptr) {
     // Synchronous response.
     auto ab = deno::ImportBuf(d, buf);
     d->current_args_->GetReturnValue().Set(ab);
     d->current_args_ = nullptr;
-    return 0;
+    return;
   }
 
   // Asynchronous response.
@@ -151,7 +151,7 @@ int deno_respond(Deno* d_, void* user_data, int32_t req_id, deno_buf buf) {
   auto recv_ = d->recv_.Get(d->isolate_);
   if (recv_.IsEmpty()) {
     d->last_exception_ = "libdeno.recv_ has not been called.";
-    return 1;
+    return;
   }
 
   v8::Local<v8::Value> args[1];
@@ -161,10 +161,7 @@ int deno_respond(Deno* d_, void* user_data, int32_t req_id, deno_buf buf) {
   if (try_catch.HasCaught()) {
     CHECK(v.IsEmpty());
     deno::HandleException(context, try_catch.Exception());
-    return 1;
   }
-
-  return 0;
 }
 
 void deno_check_promise_errors(Deno* d_) {
diff --git a/libdeno/deno.h b/libdeno/deno.h
index 42df808258..e48dd8cbe1 100644
--- a/libdeno/deno.h
+++ b/libdeno/deno.h
@@ -49,10 +49,9 @@ void deno_delete(Deno* d);
 
 // Compile and execute a traditional JavaScript script that does not use
 // module import statements.
-// Return value: 0 = fail, 1 = success
-// Get error text with deno_last_exception().
-int deno_execute(Deno* d, void* user_data, const char* js_filename,
-                 const char* js_source);
+// If it succeeded deno_last_exception() will return NULL.
+void deno_execute(Deno* d, void* user_data, const char* js_filename,
+                  const char* js_source);
 
 // deno_respond sends up to one message back for every deno_recv_cb made.
 //
@@ -70,9 +69,8 @@ int deno_execute(Deno* d, void* user_data, const char* js_filename,
 // Calling this function more than once with the same req_id will result in
 // an error.
 //
-// A non-zero return value, means a JS exception was encountered during the
-// libdeno.recv() callback. Check deno_last_exception() for exception text.
-int deno_respond(Deno* d, void* user_data, int32_t req_id, deno_buf buf);
+// If a JS exception was encountered, deno_last_exception() will be non-NULL.
+void deno_respond(Deno* d, void* user_data, int32_t req_id, deno_buf buf);
 
 void deno_check_promise_errors(Deno* d);
 
@@ -95,9 +93,11 @@ const char* deno_mod_imports_get(Deno* d, deno_mod id, size_t index);
 typedef deno_mod (*deno_resolve_cb)(void* user_data, const char* specifier,
                                     deno_mod referrer);
 
+// If it succeeded deno_last_exception() will return NULL.
 void deno_mod_instantiate(Deno* d, void* user_data, deno_mod id,
                           deno_resolve_cb cb);
 
+// If it succeeded deno_last_exception() will return NULL.
 void deno_mod_evaluate(Deno* d, void* user_data, deno_mod id);
 
 #ifdef __cplusplus
diff --git a/libdeno/libdeno_test.cc b/libdeno/libdeno_test.cc
index 5628be00e3..282a124ba9 100644
--- a/libdeno/libdeno_test.cc
+++ b/libdeno/libdeno_test.cc
@@ -4,19 +4,21 @@
 TEST(LibDenoTest, InitializesCorrectly) {
   EXPECT_NE(snapshot.data_ptr, nullptr);
   Deno* d = deno_new(deno_config{0, snapshot, empty, nullptr});
-  EXPECT_TRUE(deno_execute(d, nullptr, "a.js", "1 + 2"));
+  deno_execute(d, nullptr, "a.js", "1 + 2");
+  EXPECT_EQ(nullptr, deno_last_exception(d));
   deno_delete(d);
 }
 
 TEST(LibDenoTest, Snapshotter) {
   Deno* d1 = deno_new(deno_config{1, empty, empty, nullptr});
-  EXPECT_TRUE(deno_execute(d1, nullptr, "a.js", "a = 1 + 2"));
+  deno_execute(d1, nullptr, "a.js", "a = 1 + 2");
+  EXPECT_EQ(nullptr, deno_last_exception(d1));
   deno_buf test_snapshot = deno_get_snapshot(d1);
   deno_delete(d1);
 
   Deno* d2 = deno_new(deno_config{0, test_snapshot, empty, nullptr});
-  EXPECT_TRUE(
-      deno_execute(d2, nullptr, "b.js", "if (a != 3) throw Error('x');"));
+  deno_execute(d2, nullptr, "b.js", "if (a != 3) throw Error('x');");
+  EXPECT_EQ(nullptr, deno_last_exception(d2));
   deno_delete(d2);
 
   delete[] test_snapshot.data_ptr;
@@ -24,14 +26,16 @@ TEST(LibDenoTest, Snapshotter) {
 
 TEST(LibDenoTest, CanCallFunction) {
   Deno* d = deno_new(deno_config{0, snapshot, empty, nullptr});
-  EXPECT_TRUE(deno_execute(d, nullptr, "a.js",
-                           "if (CanCallFunction() != 'foo') throw Error();"));
+  deno_execute(d, nullptr, "a.js",
+               "if (CanCallFunction() != 'foo') throw Error();");
+  EXPECT_EQ(nullptr, deno_last_exception(d));
   deno_delete(d);
 }
 
 TEST(LibDenoTest, ErrorsCorrectly) {
   Deno* d = deno_new(deno_config{0, snapshot, empty, nullptr});
-  EXPECT_FALSE(deno_execute(d, nullptr, "a.js", "throw Error()"));
+  deno_execute(d, nullptr, "a.js", "throw Error()");
+  EXPECT_NE(nullptr, deno_last_exception(d));
   deno_delete(d);
 }
 
@@ -76,7 +80,8 @@ TEST(LibDenoTest, RecvReturnEmpty) {
     EXPECT_EQ(buf.data_ptr[2], 'c');
   };
   Deno* d = deno_new(deno_config{0, snapshot, empty, recv_cb});
-  EXPECT_TRUE(deno_execute(d, nullptr, "a.js", "RecvReturnEmpty()"));
+  deno_execute(d, nullptr, "a.js", "RecvReturnEmpty()");
+  EXPECT_EQ(nullptr, deno_last_exception(d));
   EXPECT_EQ(count, 2);
   deno_delete(d);
 }
@@ -94,14 +99,16 @@ TEST(LibDenoTest, RecvReturnBar) {
     deno_respond(d, user_data, req_id, strbuf("bar"));
   };
   Deno* d = deno_new(deno_config{0, snapshot, empty, recv_cb});
-  EXPECT_TRUE(deno_execute(d, d, "a.js", "RecvReturnBar()"));
+  deno_execute(d, d, "a.js", "RecvReturnBar()");
+  EXPECT_EQ(nullptr, deno_last_exception(d));
   EXPECT_EQ(count, 1);
   deno_delete(d);
 }
 
 TEST(LibDenoTest, DoubleRecvFails) {
   Deno* d = deno_new(deno_config{0, snapshot, empty, nullptr});
-  EXPECT_FALSE(deno_execute(d, nullptr, "a.js", "DoubleRecvFails()"));
+  deno_execute(d, nullptr, "a.js", "DoubleRecvFails()");
+  EXPECT_NE(nullptr, deno_last_exception(d));
   deno_delete(d);
 }
 
@@ -135,7 +142,8 @@ TEST(LibDenoTest, SendRecvSlice) {
     deno_respond(d, user_data, req_id, buf2);
   };
   Deno* d = deno_new(deno_config{0, snapshot, empty, recv_cb});
-  EXPECT_TRUE(deno_execute(d, d, "a.js", "SendRecvSlice()"));
+  deno_execute(d, d, "a.js", "SendRecvSlice()");
+  EXPECT_EQ(nullptr, deno_last_exception(d));
   EXPECT_EQ(count, 5);
   deno_delete(d);
 }
@@ -152,26 +160,29 @@ TEST(LibDenoTest, JSSendArrayBufferViewTypes) {
     EXPECT_EQ(buf.data_ptr[0], count);
   };
   Deno* d = deno_new(deno_config{0, snapshot, empty, recv_cb});
-  EXPECT_TRUE(deno_execute(d, nullptr, "a.js", "JSSendArrayBufferViewTypes()"));
+  deno_execute(d, nullptr, "a.js", "JSSendArrayBufferViewTypes()");
+  EXPECT_EQ(nullptr, deno_last_exception(d));
   EXPECT_EQ(count, 3);
   deno_delete(d);
 }
 
 TEST(LibDenoTest, TypedArraySnapshots) {
   Deno* d = deno_new(deno_config{0, snapshot, empty, nullptr});
-  EXPECT_TRUE(deno_execute(d, nullptr, "a.js", "TypedArraySnapshots()"));
+  deno_execute(d, nullptr, "a.js", "TypedArraySnapshots()");
+  EXPECT_EQ(nullptr, deno_last_exception(d));
   deno_delete(d);
 }
 
 TEST(LibDenoTest, SnapshotBug) {
   Deno* d = deno_new(deno_config{0, snapshot, empty, nullptr});
-  EXPECT_TRUE(deno_execute(d, nullptr, "a.js", "SnapshotBug()"));
+  deno_execute(d, nullptr, "a.js", "SnapshotBug()");
+  EXPECT_EQ(nullptr, deno_last_exception(d));
   deno_delete(d);
 }
 
 TEST(LibDenoTest, GlobalErrorHandling) {
   Deno* d = deno_new(deno_config{0, snapshot, empty, nullptr});
-  EXPECT_FALSE(deno_execute(d, nullptr, "a.js", "GlobalErrorHandling()"));
+  deno_execute(d, nullptr, "a.js", "GlobalErrorHandling()");
   std::string expected =
       "{\"message\":\"Uncaught ReferenceError: notdefined is not defined\","
       "\"sourceLine\":\" "
@@ -200,7 +211,8 @@ TEST(LibDenoTest, DataBuf) {
     EXPECT_EQ(buf.data_ptr[1], 2);
   };
   Deno* d = deno_new(deno_config{0, snapshot, empty, recv_cb});
-  EXPECT_TRUE(deno_execute(d, nullptr, "a.js", "DataBuf()"));
+  deno_execute(d, nullptr, "a.js", "DataBuf()");
+  EXPECT_EQ(nullptr, deno_last_exception(d));
   EXPECT_EQ(count, 1);
   // data_buf was subsequently changed in JS, let's check that our copy reflects
   // that.
@@ -214,7 +226,8 @@ TEST(LibDenoTest, CheckPromiseErrors) {
   auto recv_cb = [](auto _, int req_id, auto buf, auto data_buf) { count++; };
   Deno* d = deno_new(deno_config{0, snapshot, empty, recv_cb});
   EXPECT_EQ(deno_last_exception(d), nullptr);
-  EXPECT_TRUE(deno_execute(d, nullptr, "a.js", "CheckPromiseErrors()"));
+  deno_execute(d, nullptr, "a.js", "CheckPromiseErrors()");
+  EXPECT_EQ(nullptr, deno_last_exception(d));
   EXPECT_EQ(deno_last_exception(d), nullptr);
   EXPECT_EQ(count, 1);
   // We caught the exception. So still no errors after calling
@@ -227,7 +240,7 @@ TEST(LibDenoTest, CheckPromiseErrors) {
 TEST(LibDenoTest, LastException) {
   Deno* d = deno_new(deno_config{0, empty, empty, nullptr});
   EXPECT_EQ(deno_last_exception(d), nullptr);
-  EXPECT_FALSE(deno_execute(d, nullptr, "a.js", "\n\nthrow Error('boo');\n\n"));
+  deno_execute(d, nullptr, "a.js", "\n\nthrow Error('boo');\n\n");
   EXPECT_STREQ(deno_last_exception(d),
                "{\"message\":\"Uncaught Error: boo\",\"sourceLine\":\"throw "
                "Error('boo');\",\"scriptResourceName\":\"a.js\",\"lineNumber\":"
@@ -242,7 +255,7 @@ TEST(LibDenoTest, LastException) {
 TEST(LibDenoTest, EncodeErrorBug) {
   Deno* d = deno_new(deno_config{0, empty, empty, nullptr});
   EXPECT_EQ(deno_last_exception(d), nullptr);
-  EXPECT_FALSE(deno_execute(d, nullptr, "a.js", "eval('a')"));
+  deno_execute(d, nullptr, "a.js", "eval('a')");
   EXPECT_STREQ(
       deno_last_exception(d),
       "{\"message\":\"Uncaught ReferenceError: a is not "
@@ -260,7 +273,8 @@ TEST(LibDenoTest, Shared) {
   uint8_t s[] = {0, 1, 2};
   deno_buf shared = {nullptr, 0, s, 3};
   Deno* d = deno_new(deno_config{0, snapshot, shared, nullptr});
-  EXPECT_TRUE(deno_execute(d, nullptr, "a.js", "Shared()"));
+  deno_execute(d, nullptr, "a.js", "Shared()");
+  EXPECT_EQ(nullptr, deno_last_exception(d));
   EXPECT_EQ(s[0], 42);
   EXPECT_EQ(s[1], 43);
   EXPECT_EQ(s[2], 44);
diff --git a/libdeno/snapshot_creator.cc b/libdeno/snapshot_creator.cc
index d38b6c075e..ceafe0fd70 100644
--- a/libdeno/snapshot_creator.cc
+++ b/libdeno/snapshot_creator.cc
@@ -26,8 +26,8 @@ int main(int argc, char** argv) {
   deno_config config = {1, deno::empty_buf, deno::empty_buf, nullptr};
   Deno* d = deno_new(config);
 
-  int r = deno_execute(d, nullptr, js_fn, js_source.c_str());
-  if (!r) {
+  deno_execute(d, nullptr, js_fn, js_source.c_str());
+  if (deno_last_exception(d) != nullptr) {
     std::cerr << "Snapshot Exception " << std::endl;
     std::cerr << deno_last_exception(d) << std::endl;
     deno_delete(d);
diff --git a/src/isolate.rs b/src/isolate.rs
index 0f64d5ab4a..e0a657ff2d 100644
--- a/src/isolate.rs
+++ b/src/isolate.rs
@@ -251,7 +251,7 @@ impl Isolate {
   ) -> Result<(), JSError> {
     let filename = CString::new(js_filename).unwrap();
     let source = CString::new(js_source).unwrap();
-    let r = unsafe {
+    unsafe {
       libdeno::deno_execute(
         self.libdeno_isolate,
         self.as_raw_ptr(),
@@ -259,9 +259,8 @@ impl Isolate {
         source.as_ptr(),
       )
     };
-    if r == 0 {
-      let js_error = self.last_exception().unwrap();
-      return Err(js_error);
+    if let Some(err) = self.last_exception() {
+      return Err(err);
     }
     Ok(())
   }
diff --git a/src/libdeno.rs b/src/libdeno.rs
index ac1655bb3f..ddf025aba9 100644
--- a/src/libdeno.rs
+++ b/src/libdeno.rs
@@ -148,7 +148,7 @@ extern "C" {
     user_data: *const c_void,
     js_filename: *const c_char,
     js_source: *const c_char,
-  ) -> c_int;
+  );
 
   // Modules