diff --git a/t/test-lib-functions.sh b/t/test-lib-functions.sh
index 8889ba5104..7c4c633592 100644
--- a/t/test-lib-functions.sh
+++ b/t/test-lib-functions.sh
@@ -135,12 +135,12 @@ test_pause () {
 	fi
 }
 
-# Call test_commit with the arguments "<message> [<file> [<contents>]]"
+# Call test_commit with the arguments "<message> [<file> [<contents> [<tag>]]]"
 #
 # This will commit a file with the given contents and the given commit
-# message.  It will also add a tag with <message> as name.
+# message, and tag the resulting commit with the given tag name.
 #
-# Both <file> and <contents> default to <message>.
+# <file>, <contents>, and <tag> all default to <message>.
 
 test_commit () {
 	notick= &&
@@ -168,7 +168,7 @@ test_commit () {
 		test_tick
 	fi &&
 	git commit $signoff -m "$1" &&
-	git tag "$1"
+	git tag "${4:-$1}"
 }
 
 # Call test_merge with the arguments "<message> <commit>", where <commit>