diff --git a/main/strings.c b/main/strings.c
index aecf4099ec78a8b8c006811ee3663db32efa1c53..2e4b749c97c3deaf71867a54f6bfc08c5f339834 100644
--- a/main/strings.c
+++ b/main/strings.c
@@ -143,7 +143,8 @@ char *__ast_str_helper2(struct ast_str **buf, size_t maxlen, const char *src, si
 		maxlen--;
 		(*buf)->__AST_STR_USED++;
 
-		if (dynamic && (!maxlen || (escapecommas && !(maxlen - 1)))) {
+		if ((ptr >= (*buf)->__AST_STR_STR + (*buf)->__AST_STR_LEN - 3) ||
+			(dynamic && (!maxlen || (escapecommas && !(maxlen - 1))))) {
 			char *oldbase = (*buf)->__AST_STR_STR;
 			size_t old = (*buf)->__AST_STR_LEN;
 			if (ast_str_make_space(buf, (*buf)->__AST_STR_LEN * 2)) {