diff --git a/src/wn.c b/src/wn.c
index ddb27aa..b160392 100644
--- a/src/wn.c
+++ b/src/wn.c
@@ -344,7 +344,7 @@ static int getoptidx(char *searchtype)

 static int error_message(char *msg)
 {
-    fprintf(stderr, msg);
+    fprintf(stderr, "%s", msg);
     return(0);
 }