diff --git a/src/diag_msg.c b/src/diag_msg.c
index e96ad7a..20eca83 100644
--- a/src/diag_msg.c
+++ b/src/diag_msg.c
@@ -102,7 +102,7 @@
 		file, osmo_load16le(&msg->line_nr));
 
 	/* replace all '%s' with '%p', as %s obviously doesn't work */
-	for (char *cur = fmt; cur && (cur < fmt + strlen(fmt)); cur = strstr(fmt, "%s")) {
+	for (char *cur = strstr(fmt, "%s"); cur && (cur < fmt + strlen(fmt)); cur = strstr(fmt, "%s")) {
 		cur[1] = 'p';
 	}