diff --git a/builtin/mktag.c b/builtin/mktag.c
index 4982d3a93e..ff7ac8e0e5 100644
--- a/builtin/mktag.c
+++ b/builtin/mktag.c
@@ -161,7 +161,7 @@ int cmd_mktag(int argc, const char **argv, const char *prefix)
 	if (argc != 1)
 		usage("git mktag");
 
-	if (strbuf_read(&buf, 0, 4096) < 0) {
+	if (strbuf_read(&buf, 0, 0) < 0) {
 		die_errno("could not read from stdin");
 	}