diff --git a/src/openvpn/options.c b/src/openvpn/options.c
index 8978955c3..5ecb7b7db 100644
--- a/src/openvpn/options.c
+++ b/src/openvpn/options.c
@@ -2077,7 +2077,7 @@ check_ca_required(const struct options *options)
         " or CA path (--capath)"
 #endif
         " and/or peer fingerprint verification (--peer-fingerprint)";
-    msg(M_USAGE, str);
+    msg(M_USAGE, "%s", str);
 }
 
 static void