diff --git a/ripngd/ripng_main.c b/ripngd/ripng_main.c
index 9219378..40d2b14 100644
--- a/ripngd/ripng_main.c
+++ b/ripngd/ripng_main.c
@@ -96,7 +96,7 @@
 struct thread_master *master;
 
 /* Process ID saved for use by init system */
-char *pid_file = PATH_RIPNGD_PID;
+const char *pid_file = PATH_RIPNGD_PID;
 
 /* Help information display. */
 static void