diff --git a/Documentation/git-patch-id.adoc b/Documentation/git-patch-id.adoc
index abd02fccdc..61498def31 100644
--- a/Documentation/git-patch-id.adoc
+++ b/Documentation/git-patch-id.adoc
@@ -21,7 +21,7 @@ the same time also reasonably unique, i.e., two patches that have the same
 
 The main usecase for this command is to look for likely duplicate commits.
 
-When dealing with `git diff-tree` output, it takes advantage of
+When dealing with `git diff-tree --patch` output, it takes advantage of
 the fact that the patch is prefixed with the object name of the
 commit, and outputs two 40-byte hexadecimal strings.  The first
 string is the patch ID, and the second string is the commit ID.