diff --git a/ChangeLog b/ChangeLog
index 1f10534e..58a9382a 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+2011-07-30  Nicolas François  <nicolas.francois@centraliens.net>
+
+	* lib/commonio.c: Display PID as unsigned long.
+
 2011-07-30  Nicolas François  <nicolas.francois@centraliens.net>
 
 	* src/useradd.c: Remove unused Zflg.
diff --git a/lib/commonio.c b/lib/commonio.c
index 603ac3c7..33b92f35 100644
--- a/lib/commonio.c
+++ b/lib/commonio.c
@@ -216,8 +216,8 @@ static int do_lock_file (const char *file, const char *lock, bool log)
 	if (kill (pid, 0) == 0) {
 		if (log) {
 			(void) fprintf (stderr,
-			                "%s: lock %s already used by PID %d\n",
-			                Prog, lock, pid);
+			                "%s: lock %s already used by PID %lu\n",
+			                Prog, lock, (unsigned long) pid);
 		}
 		unlink (file);
 		errno = EEXIST;