--- src/libspf2/spf_dns.c.orig	Wed Apr 19 18:35:29 2017
+++ src/libspf2/spf_dns.c	Wed Apr 19 18:35:40 2017
@@ -105,7 +105,7 @@ SPF_dns_debug_post(SPF_dns_server_t *spf_dns_server, S
 					break;
 
 				default:
-					SPF_debugf("    - Unknown RR type");
+					SPF_debugf("%s", "    - Unknown RR type");
 					break;
 			}
 		}