diff --git a/runtime/trampolines-invoke.m b/runtime/trampolines-invoke.m
index 6b76b3ae9439..3834480cbe55 100644
--- a/runtime/trampolines-invoke.m
+++ b/runtime/trampolines-invoke.m
@@ -50,7 +50,7 @@
 	if (obj == NULL)
 		return NULL;
 
-	char *str = mono_string_to_utf8 ((MonoString *) obj);
+	char *str = mono_string_to_utf8 (obj);
 	NSString *arg;
 	if (retain) {
 		arg = [[NSString alloc] initWithUTF8String:str];