diff --git a/Documentation/git-diff-index.txt b/Documentation/git-diff-index.txt
index f4bd8155c0..25fe165f00 100644
--- a/Documentation/git-diff-index.txt
+++ b/Documentation/git-diff-index.txt
@@ -27,7 +27,7 @@ include::diff-options.txt[]
 	The id of a tree object to diff against.
 
 --cached::
-	do not consider the on-disk file at all
+	Do not consider the on-disk file at all.
 
 -m::
 	By default, files recorded in the index but not checked