--- a/src/c/alloc_2.d
+++ b/src/c/alloc_2.d
@@ -34,7 +34,7 @@
 static void (*GC_old_start_callback)(void) = NULL;
 #ifdef HAVE_GC_SET_START_CALLBACK
 extern void GC_set_start_callback(void *);
-extern void *GC_get_start_callback(void *);
+extern void *GC_get_start_callback();
 #else
 extern void (*GC_start_call_back)(void);
 #endif