diff --git a/builtin/pack-objects.c b/builtin/pack-objects.c
index e50c6cd1ff..4eac2f997b 100644
--- a/builtin/pack-objects.c
+++ b/builtin/pack-objects.c
@@ -3252,7 +3252,7 @@ int cmd_pack_objects(int argc, const char **argv, const char *prefix)
 			 N_("similar to --all-progress when progress meter is shown")),
 		{ OPTION_CALLBACK, 0, "index-version", NULL, N_("<version>[,<offset>]"),
 		  N_("write the pack index file in the specified idx format version"),
-		  0, option_parse_index_version },
+		  PARSE_OPT_NONEG, option_parse_index_version },
 		OPT_MAGNITUDE(0, "max-pack-size", &pack_size_limit,
 			      N_("maximum size of each output pack file")),
 		OPT_BOOL(0, "local", &local,