diff --git a/include/__threading_support b/include/__threading_support
index 097cb73..589fe20 100644
--- a/include/__threading_support
+++ b/include/__threading_support
@@ -158,7 +158,7 @@
 // Execute once
 _LIBCPP_THREAD_ABI_VISIBILITY
 int __libcpp_execute_once(__libcpp_exec_once_flag *flag,
-                          void (*init_routine)(void));
+                          void (*init_routine)());
 
 // Thread id
 _LIBCPP_THREAD_ABI_VISIBILITY
@@ -301,7 +301,7 @@
 
 // Execute once
 int __libcpp_execute_once(__libcpp_exec_once_flag *flag,
-                          void (*init_routine)(void)) {
+                          void (*init_routine)()) {
   return pthread_once(flag, init_routine);
 }