diff --git a/lib-src/emacsclient.c b/lib-src/emacsclient.c
index b86277844c9..92f19d4746c 100644
--- a/lib-src/emacsclient.c
+++ b/lib-src/emacsclient.c
@@ -280,7 +280,7 @@ quote_argument (str, stream)
     }
   *q++ = 0;
 
-  fprintf (stream, copy);
+  fprintf (stream, "%s", copy);
 
   free (copy);
 }