diff --git a/channels/chan_iax2.c b/channels/chan_iax2.c
index 3c2f80406f..287ad2e0ce 100644
--- a/channels/chan_iax2.c
+++ b/channels/chan_iax2.c
@@ -1411,7 +1411,7 @@ static int try_firmware(char *s)
 		return -1;
 	}
 	fwh = mmap(NULL, stbuf.st_size, PROT_READ, MAP_PRIVATE, fd, 0); 
-	if (!fwh) {
+	if (fwh == (void *) -1) {
 		ast_log(LOG_WARNING, "mmap failed: %s\n", strerror(errno));
 		close(fd);
 		return -1;