diff --git a/lib/roken/vsyslog.c b/lib/roken/vsyslog.c
index 98dc2b021..6b7da5d6c 100644
--- a/lib/roken/vsyslog.c
+++ b/lib/roken/vsyslog.c
@@ -88,6 +88,7 @@ vsyslog(int pri, const char *fmt, va_list ap)
 	} else
 	    *p2++ = *p;
     }
+    *p2 = '\0';
 
     vasprintf (&buf, fmt2, ap);
     free (fmt2);