diff --git a/runtime/bin/file.cc b/runtime/bin/file.cc
index 0bc02c01f6e..cdbbc959f73 100644
--- a/runtime/bin/file.cc
+++ b/runtime/bin/file.cc
@@ -113,12 +113,15 @@ void FUNCTION_NAME(File_Open)(Dart_NativeArguments args) {
 }
 
 void FUNCTION_NAME(File_Exists)(Dart_NativeArguments args) {
-  Namespace* namespc = Namespace::GetNamespace(args, 0);
-  Dart_Handle path_handle = Dart_GetNativeArgument(args, 1);
-  TypedDataScope data(path_handle);
-  ASSERT(data.type() == Dart_TypedData_kUint8);
-  const char* filename = data.GetCString();
-  bool exists = File::Exists(namespc, filename);
+  bool exists;
+  {
+    Namespace* namespc = Namespace::GetNamespace(args, 0);
+    Dart_Handle path_handle = Dart_GetNativeArgument(args, 1);
+    TypedDataScope data(path_handle);
+    ASSERT(data.type() == Dart_TypedData_kUint8);
+    const char* filename = data.GetCString();
+    exists = File::Exists(namespc, filename);
+  }
   Dart_SetBooleanReturnValue(args, exists);
 }
 
@@ -710,13 +713,16 @@ void FUNCTION_NAME(File_GetStdioHandleType)(Dart_NativeArguments args) {
 }
 
 void FUNCTION_NAME(File_GetType)(Dart_NativeArguments args) {
-  Namespace* namespc = Namespace::GetNamespace(args, 0);
-  Dart_Handle path_handle = Dart_GetNativeArgument(args, 1);
-  TypedDataScope data(path_handle);
-  ASSERT(data.type() == Dart_TypedData_kUint8);
-  const char* path = data.GetCString();
-  bool follow_links = DartUtils::GetNativeBooleanArgument(args, 2);
-  File::Type type = File::GetType(namespc, path, follow_links);
+  File::Type type;
+  {
+    Namespace* namespc = Namespace::GetNamespace(args, 0);
+    Dart_Handle path_handle = Dart_GetNativeArgument(args, 1);
+    TypedDataScope data(path_handle);
+    ASSERT(data.type() == Dart_TypedData_kUint8);
+    const char* path = data.GetCString();
+    bool follow_links = DartUtils::GetNativeBooleanArgument(args, 2);
+    type = File::GetType(namespc, path, follow_links);
+  }
   Dart_SetIntegerReturnValue(args, static_cast<int>(type));
 }
 
diff --git a/runtime/bin/sync_socket.cc b/runtime/bin/sync_socket.cc
index 12b1fee76a6..4589d4a1281 100644
--- a/runtime/bin/sync_socket.cc
+++ b/runtime/bin/sync_socket.cc
@@ -141,13 +141,13 @@ void FUNCTION_NAME(SynchronousSocket_WriteList)(Dart_NativeArguments args) {
   buffer += offset;
   intptr_t bytes_written =
       SynchronousSocket::Write(socket->fd(), buffer, length);
+  Dart_TypedDataReleaseData(buffer_obj);
   if (bytes_written >= 0) {
     Dart_SetIntegerReturnValue(args, bytes_written);
   } else {
     OSError os_error;
     Dart_SetReturnValue(args, DartUtils::NewDartOSError(&os_error));
   }
-  Dart_TypedDataReleaseData(buffer_obj);
 }
 
 void FUNCTION_NAME(SynchronousSocket_ReadList)(Dart_NativeArguments args) {
diff --git a/runtime/vm/dart_api_impl.cc b/runtime/vm/dart_api_impl.cc
index b01af49f2f0..4f304d966d3 100644
--- a/runtime/vm/dart_api_impl.cc
+++ b/runtime/vm/dart_api_impl.cc
@@ -4712,6 +4712,7 @@ DART_EXPORT void Dart_SetReturnValue(Dart_NativeArguments args,
                                      Dart_Handle retval) {
   NativeArguments* arguments = reinterpret_cast<NativeArguments*>(args);
   ASSERT(arguments->thread()->isolate() == Isolate::Current());
+  ASSERT_CALLBACK_STATE(arguments->thread());
   if ((retval != Api::Null()) && !Api::IsInstance(retval) &&
       !Api::IsError(retval)) {
     // Print the current stack trace to make the problematic caller
@@ -4832,6 +4833,8 @@ Dart_SetEnvironmentCallback(Dart_EnvironmentCallback callback) {
 DART_EXPORT void Dart_SetBooleanReturnValue(Dart_NativeArguments args,
                                             bool retval) {
   NativeArguments* arguments = reinterpret_cast<NativeArguments*>(args);
+  ASSERT(arguments->thread()->isolate() == Isolate::Current());
+  ASSERT_CALLBACK_STATE(arguments->thread());
   arguments->SetReturn(Bool::Get(retval));
 }
 
@@ -4839,6 +4842,7 @@ DART_EXPORT void Dart_SetIntegerReturnValue(Dart_NativeArguments args,
                                             int64_t retval) {
   NativeArguments* arguments = reinterpret_cast<NativeArguments*>(args);
   ASSERT(arguments->thread()->isolate() == Isolate::Current());
+  ASSERT_CALLBACK_STATE(arguments->thread());
   if (Smi::IsValid(retval)) {
     Api::SetSmiReturnValue(arguments, static_cast<intptr_t>(retval));
   } else {
@@ -4852,6 +4856,7 @@ DART_EXPORT void Dart_SetIntegerReturnValue(Dart_NativeArguments args,
 DART_EXPORT void Dart_SetDoubleReturnValue(Dart_NativeArguments args,
                                            double retval) {
   NativeArguments* arguments = reinterpret_cast<NativeArguments*>(args);
+  ASSERT(arguments->thread()->isolate() == Isolate::Current());
   ASSERT_CALLBACK_STATE(arguments->thread());
   TransitionNativeToVM transition(arguments->thread());
   Api::SetDoubleReturnValue(arguments, retval);