diff --git a/pri_internal.h b/pri_internal.h
index 8c8ff71..4cb2413 100644
--- a/pri_internal.h
+++ b/pri_internal.h
@@ -287,9 +287,8 @@ extern void pri_schedule_del(struct pri *pri, int ev);
 
 extern pri_event *pri_mkerror(struct pri *pri, char *errstr);
 
-extern void pri_message(struct pri *pri, char *fmt, ...);
-
-extern void pri_error(struct pri *pri, char *fmt, ...);
+void pri_message(struct pri *ctrl, char *fmt, ...) __attribute__((format(printf, 2, 3)));
+void pri_error(struct pri *ctrl, char *fmt, ...) __attribute__((format(printf, 2, 3)));
 
 void libpri_copy_string(char *dst, const char *src, size_t size);
 
diff --git a/q931.c b/q931.c
index 5553d4b..8ab7d98 100644
--- a/q931.c
+++ b/q931.c
@@ -682,7 +682,8 @@ static void dump_bearer_capability(int full_ie, struct pri *ctrl, q931_ie *ie, i
 					(data & 0x04)?1:0,
 					(data & 0x02)?1:0);
 			} else {
-				pri_message(ctrl, "%c                                Unknown octet 5b: 0x%x\n", data );
+				pri_message(ctrl, "%c                                Unknown octet 5b: 0x%x\n",
+					prefix, data);
 			}
 			pos++;
 		}
@@ -1970,12 +1971,13 @@ static void dump_generic_digits(int full_ie, struct pri *ctrl, q931_ie *ie, int
 	type = ie->data[0] & 0x1F;
 	pri_message(ctrl, "%c Generic Digits (len=%02d): Encoding %s  Type %s\n", prefix, len, gdencoding2str(encoding), gdtype2str(type));
 	if (encoding == 3) {	/* Binary */
-		pri_message(ctrl, "%c                            Don't know how to handle binary encoding\n");
+		pri_message(ctrl, "%c                            Don't know how to handle binary encoding\n",
+			prefix);
 		return;
 	}
 	if (len == 3)	/* No number information */
 		return;
-	pri_message(ctrl, "%c                            Digits: ");
+	pri_message(ctrl, "%c                            Digits: ", prefix);
 	value = 0;
 	for(idx = 3; idx < len; ++idx) {
 		switch(encoding) {