diff --git a/src/apps/gbasm.c b/src/apps/gbasm.c
index 922d6de..1788d10 100644
--- a/src/apps/gbasm.c
+++ b/src/apps/gbasm.c
@@ -39,7 +39,7 @@ int main(int argc, char **argv)
 				close(out_fd);
 			}
 
-			out_fd = open(optarg, O_WRONLY | O_CREAT);
+			out_fd = open(optarg, O_WRONLY | O_CREAT | O_TRUNC);
 			if (out_fd < 0) {
 				fprintf(stderr, "failed to open output file %s\n", optarg);
 				exit(1);