diff --git a/channels/chan_zap.c b/channels/chan_zap.c
index bdc786fa99..556cdc59c6 100644
--- a/channels/chan_zap.c
+++ b/channels/chan_zap.c
@@ -7163,8 +7163,10 @@ static void *do_monitor(void *data)
 		/* Lock the interface list */
 		ast_mutex_lock(&iflock);
 		if (!pfds || (lastalloc != ifcount)) {
-			if (pfds)
+			if (pfds) {
 				ast_free(pfds);
+				pfds = NULL;
+			}
 			if (ifcount) {
 				if (!(pfds = ast_calloc(1, ifcount * sizeof(*pfds)))) {
 					ast_mutex_unlock(&iflock);