--- a/git-subtree
+++ b/git-subtree
@@ -339,7 +339,13 @@ cache_set () {
		test "$oldrev" != "latest_new" &&
		test -e "$cachedir/$oldrev"
	then
-		die "fatal: cache for $oldrev already exists!"
+		existing=$(cat "$cachedir/$oldrev")
+		if test "$existing" = "$newrev"
+		then
+			return
+		else
+			die "fatal: cache for $oldrev already exists!"
+		fi
	fi
	echo "$newrev" >"$cachedir/$oldrev"
}