diff --git a/libdeno/binding.cc b/libdeno/binding.cc
index 55a78069e8..c5f582aaee 100644
--- a/libdeno/binding.cc
+++ b/libdeno/binding.cc
@@ -243,7 +243,7 @@ void Send(const v8::FunctionCallbackInfo<v8::Value>& args) {
   DCHECK_EQ(d->currentArgs, nullptr);
   d->currentArgs = &args;
 
-  d->cb(d, req_id, control, data);
+  d->cb(d->user_data, req_id, control, data);
 
   if (d->currentArgs == nullptr) {
     // This indicates that deno_repond() was called already.
@@ -431,11 +431,6 @@ void deno_init() {
   v8::V8::Initialize();
 }
 
-void* deno_get_data(const Deno* d) {
-  CHECK(d->user_data != nullptr);
-  return d->user_data;
-}
-
 const char* deno_v8_version() { return v8::V8::GetVersion(); }
 
 void deno_set_v8_flags(int* argc, char** argv) {
diff --git a/libdeno/deno.h b/libdeno/deno.h
index c166c7fde2..5fad6a1c32 100644
--- a/libdeno/deno.h
+++ b/libdeno/deno.h
@@ -23,8 +23,8 @@ typedef struct deno_s Deno;
 // A callback to receive a message from a libdeno.send() javascript call.
 // control_buf is valid for only for the lifetime of this callback.
 // data_buf is valid until deno_respond() is called.
-typedef void (*deno_recv_cb)(Deno* d, int32_t req_id, deno_buf control_buf,
-                             deno_buf data_buf);
+typedef void (*deno_recv_cb)(void* user_data, int32_t req_id,
+                             deno_buf control_buf, deno_buf data_buf);
 
 void deno_init();
 const char* deno_v8_version();
@@ -33,9 +33,6 @@ void deno_set_v8_flags(int* argc, char** argv);
 Deno* deno_new(deno_recv_cb cb);
 void deno_delete(Deno* d);
 
-// Returns the void* user_data provided in deno_new.
-void* deno_get_data(Deno*);
-
 // Returns false on error.
 // Get error text with deno_last_exception().
 // 0 = fail, 1 = success
diff --git a/libdeno/libdeno_test.cc b/libdeno/libdeno_test.cc
index 2748a60cce..e46c629786 100644
--- a/libdeno/libdeno_test.cc
+++ b/libdeno/libdeno_test.cc
@@ -69,16 +69,17 @@ TEST(LibDenoTest, RecvReturnEmpty) {
 
 TEST(LibDenoTest, RecvReturnBar) {
   static int count = 0;
-  Deno* d = deno_new([](auto deno, int req_id, auto buf, auto data_buf) {
+  Deno* d = deno_new([](auto user_data, int req_id, auto buf, auto data_buf) {
+    auto d = reinterpret_cast<Deno*>(user_data);
     assert_null(data_buf);
     count++;
     EXPECT_EQ(static_cast<size_t>(3), buf.data_len);
     EXPECT_EQ(buf.data_ptr[0], 'a');
     EXPECT_EQ(buf.data_ptr[1], 'b');
     EXPECT_EQ(buf.data_ptr[2], 'c');
-    deno_respond(deno, nullptr, req_id, strbuf("bar"));
+    deno_respond(d, user_data, req_id, strbuf("bar"));
   });
-  EXPECT_TRUE(deno_execute(d, nullptr, "a.js", "RecvReturnBar()"));
+  EXPECT_TRUE(deno_execute(d, d, "a.js", "RecvReturnBar()"));
   EXPECT_EQ(count, 1);
   deno_delete(d);
 }
@@ -91,7 +92,8 @@ TEST(LibDenoTest, DoubleRecvFails) {
 
 TEST(LibDenoTest, SendRecvSlice) {
   static int count = 0;
-  Deno* d = deno_new([](auto deno, int req_id, auto buf, auto data_buf) {
+  Deno* d = deno_new([](auto user_data, int req_id, auto buf, auto data_buf) {
+    auto d = reinterpret_cast<Deno*>(user_data);
     assert_null(data_buf);
     static const size_t alloc_len = 1024;
     size_t i = count++;
@@ -115,9 +117,9 @@ TEST(LibDenoTest, SendRecvSlice) {
     buf2.data_ptr[0] = 200 + i;
     buf2.data_ptr[buf2.data_len - 1] = 200 - i;
     // Send back.
-    deno_respond(deno, nullptr, req_id, buf2);
+    deno_respond(d, user_data, req_id, buf2);
   });
-  EXPECT_TRUE(deno_execute(d, nullptr, "a.js", "SendRecvSlice()"));
+  EXPECT_TRUE(deno_execute(d, d, "a.js", "SendRecvSlice()"));
   EXPECT_EQ(count, 5);
   deno_delete(d);
 }
diff --git a/src/isolate.rs b/src/isolate.rs
index 8f8e798fb1..dc44b11e2c 100644
--- a/src/isolate.rs
+++ b/src/isolate.rs
@@ -100,8 +100,8 @@ impl Isolate {
     self as *mut _ as *mut c_void
   }
 
-  pub fn from_c<'a>(d: *const libdeno::isolate) -> &'a mut Isolate {
-    let ptr = unsafe { libdeno::deno_get_data(d) } as *mut _;
+  pub fn from_void_ptr<'a>(ptr: *mut c_void) -> &'a mut Isolate {
+    let ptr = ptr as *mut _;
     unsafe { &mut *ptr }
   }
 
@@ -236,7 +236,7 @@ impl From<Buf> for libdeno::deno_buf {
 
 // Dereferences the C pointer into the Rust Isolate object.
 extern "C" fn pre_dispatch(
-  d: *const libdeno::isolate,
+  user_data: *mut c_void,
   req_id: i32,
   control_buf: libdeno::deno_buf,
   data_buf: libdeno::deno_buf,
@@ -256,7 +256,7 @@ extern "C" fn pre_dispatch(
     )
   };
 
-  let isolate = Isolate::from_c(d);
+  let isolate = Isolate::from_void_ptr(user_data);
   let dispatch = isolate.dispatch;
   let (is_sync, op) = dispatch(isolate, control_slice, data_slice);
 
diff --git a/src/libdeno.rs b/src/libdeno.rs
index 77f7f5c3ef..4417ac5448 100644
--- a/src/libdeno.rs
+++ b/src/libdeno.rs
@@ -20,7 +20,7 @@ pub struct deno_buf {
 }
 
 type DenoRecvCb = unsafe extern "C" fn(
-  d: *const isolate,
+  user_data: *mut c_void,
   req_id: i32,
   buf: deno_buf,
   data_buf: deno_buf,
@@ -33,7 +33,6 @@ extern "C" {
   pub fn deno_new(cb: DenoRecvCb) -> *const isolate;
   pub fn deno_delete(i: *const isolate);
   pub fn deno_last_exception(i: *const isolate) -> *const c_char;
-  pub fn deno_get_data(i: *const isolate) -> *mut c_void;
   pub fn deno_respond(
     i: *const isolate,
     user_data: *mut c_void,