diff --git a/src/proto/os_unix.pro b/src/proto/os_unix.pro
index 4677eb0..721c07d 100644
--- a/src/proto/os_unix.pro
+++ b/src/proto/os_unix.pro
@@ -27,7 +27,7 @@
 int mch_get_uname(uid_t uid, char_u *s, int len);
 void mch_get_host_name(char_u *s, int len);
 long mch_get_pid(void);
-int mch_process_running(pid_t pid);
+int mch_process_running(long pid);
 int mch_dirname(char_u *buf, int len);
 int mch_FullName(char_u *fname, char_u *buf, int len, int force);
 int mch_isFullName(char_u *fname);