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);

 }