diff --git a/Modules/_posixsubprocess.c b/Modules/_posixsubprocess.c
index c8f2500..babf039 100644
--- a/Modules/_posixsubprocess.c
+++ b/Modules/_posixsubprocess.c
@@ -80,7 +80,7 @@
  * that properly supports /dev/fd.
  */
 static int
-_is_fdescfs_mounted_on_dev_fd()
+_is_fdescfs_mounted_on_dev_fd(void)
 {
     struct stat dev_stat;
     struct stat dev_fd_stat;