diff --git a/builtin/add.c b/builtin/add.c
index 12247b4..d461ba0 100644
--- a/builtin/add.c
+++ b/builtin/add.c
@@ -239,7 +239,7 @@
 	rev.diffopt.output_format = DIFF_FORMAT_PATCH;
 	rev.diffopt.use_color = 0;
 	rev.diffopt.flags.ignore_dirty_submodules = 1;
-	out = open(file, O_CREAT | O_WRONLY, 0666);
+	out = open(file, O_CREAT | O_WRONLY | O_TRUNC, 0666);
 	if (out < 0)
 		die(_("Could not open '%s' for writing."), file);
 	rev.diffopt.file = xfdopen(out, "w");