diff --git a/builtin/checkout.c b/builtin/checkout.c
index 21bac3a561..99b873d3cd 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -566,6 +566,14 @@ static int skip_merge_working_tree(const struct checkout_opts *opts,
 	 * Remaining variables are not checkout options but used to track state
 	 */
 
+	 /*
+	  * Do the merge if this is the initial checkout. We cannot use
+	  * is_cache_unborn() here because the index hasn't been loaded yet
+	  * so cache_nr and timestamp.sec are always zero.
+	  */
+	if (!file_exists(get_index_file()))
+		return 0;
+
 	return 1;
 }
 
diff --git a/t/t2018-checkout-branch.sh b/t/t2018-checkout-branch.sh
index 6da2d4e68f..c5014ad9a6 100755
--- a/t/t2018-checkout-branch.sh
+++ b/t/t2018-checkout-branch.sh
@@ -198,7 +198,7 @@ test_expect_success 'checkout -B to the current branch works' '
 	test_dirty_mergeable
 '
 
-test_expect_failure 'checkout -b after clone --no-checkout does a checkout of HEAD' '
+test_expect_success 'checkout -b after clone --no-checkout does a checkout of HEAD' '
 	git init src &&
 	test_commit -C src a &&
 	rev="$(git -C src rev-parse HEAD)" &&