diff --git a/contrib/subtree/git-subtree.sh b/contrib/subtree/git-subtree.sh
index fa1a5839af..39c7d54ce8 100755
--- a/contrib/subtree/git-subtree.sh
+++ b/contrib/subtree/git-subtree.sh
@@ -298,7 +298,7 @@ copy_commit()
 	# We're going to set some environment vars here, so
 	# do it in a subshell to get rid of them safely later
 	debug copy_commit "{$1}" "{$2}" "{$3}"
-	git log -1 --pretty=format:'%an%n%ae%n%ad%n%cn%n%ce%n%cd%n%B' "$1" |
+	git log -1 --pretty=format:'%an%n%ae%n%aD%n%cn%n%ce%n%cD%n%B' "$1" |
 	(
 		read GIT_AUTHOR_NAME
 		read GIT_AUTHOR_EMAIL
diff --git a/contrib/subtree/t/t7900-subtree.sh b/contrib/subtree/t/t7900-subtree.sh
index 6309d124ca..da709f96e5 100755
--- a/contrib/subtree/t/t7900-subtree.sh
+++ b/contrib/subtree/t/t7900-subtree.sh
@@ -94,6 +94,10 @@ test_expect_success 'add sub3' '
 # Back to mainline
 cd ..
 
+test_expect_success 'enable log.date=relative to catch errors' '
+	git config log.date relative
+'
+
 test_expect_success 'add main4' '
         create main4 &&
         git commit -m "main4" &&