diff --git a/Documentation/git-show-index.txt b/Documentation/git-show-index.txt
index e49318a5a0..7e574ea243 100644
--- a/Documentation/git-show-index.txt
+++ b/Documentation/git-show-index.txt
@@ -9,7 +9,7 @@ git-show-index - Show packed archive index
 SYNOPSIS
 --------
 [verse]
-'git show-index' [--object-format=<hash-algorithm>]
+'git show-index' [--object-format=<hash-algorithm>] < <pack-idx-file>
 
 
 DESCRIPTION
diff --git a/builtin/show-index.c b/builtin/show-index.c
index 756d632b51..9d4ecf5e7b 100644
--- a/builtin/show-index.c
+++ b/builtin/show-index.c
@@ -9,7 +9,7 @@
 #include "parse-options.h"
 
 static const char *const show_index_usage[] = {
-	"git show-index [--object-format=<hash-algorithm>]",
+	"git show-index [--object-format=<hash-algorithm>] < <pack-idx-file>",
 	NULL
 };