diff --git a/pbx.c b/pbx.c
index bdd62dd0ea..0aaea68cce 100644
--- a/pbx.c
+++ b/pbx.c
@@ -4346,6 +4346,7 @@ int ast_add_extension2(struct ast_context *con,
 	tmp->registrar = registrar;
 
 	ast_mutex_lock(&con->lock);
+	res = 0; /* some compilers will think it is uninitialized otherwise */
 	for (e = con->root; e; el = e, e = e->next) {   /* scan the extension list */
 		res = ext_cmp(e->exten, extension);
 		if (res == 0) { /* extension match, now look at cidmatch */