diff --git a/t/lib-submodule-update.sh b/t/lib-submodule-update.sh
index f2e58eb904..759dbe614c 100755
--- a/t/lib-submodule-update.sh
+++ b/t/lib-submodule-update.sh
@@ -285,7 +285,16 @@ test_submodule_switch () {
 	'
 	# ... as does removing a directory with tracked files with a
 	# submodule.
-	test_expect_success "$command: replace directory with submodule" '
+	if test "$KNOWN_FAILURE_NOFF_MERGE_DOESNT_CREATE_EMPTY_SUBMODULE_DIR" = 1
+	then
+		# Non fast-forward merges fail with "Directory sub1 doesn't
+		# exist. sub1" because the empty submodule directory is not
+		# created
+		RESULT="failure"
+	else
+		RESULT="success"
+	fi
+	test_expect_$RESULT "$command: replace directory with submodule" '
 		prolog &&
 		reset_work_tree_to replace_sub1_with_directory &&
 		(
@@ -328,7 +337,16 @@ test_submodule_switch () {
 	'
 	# Replacing a submodule with files in a directory must fail as the
 	# submodule work tree isn't removed ...
-	test_expect_success "$command: replace submodule with a directory must fail" '
+	if test "$KNOWN_FAILURE_NOFF_MERGE_ATTEMPTS_TO_MERGE_REMOVED_SUBMODULE_FILES" = 1
+	then
+		# Non fast-forward merges attempt to merge the former
+		# submodule files with the newly checked out ones in the
+		# directory of the same name while it shouldn't.
+		RESULT="failure"
+	else
+		RESULT="success"
+	fi
+	test_expect_$RESULT "$command: replace submodule with a directory must fail" '
 		prolog &&
 		reset_work_tree_to add_sub1 &&
 		(
@@ -340,7 +358,7 @@ test_submodule_switch () {
 		)
 	'
 	# ... especially when it contains a .git directory.
-	test_expect_success "$command: replace submodule containing a .git directory with a directory must fail" '
+	test_expect_$RESULT "$command: replace submodule containing a .git directory with a directory must fail" '
 		prolog &&
 		reset_work_tree_to add_sub1 &&
 		(
diff --git a/t/t7613-merge-submodule.sh b/t/t7613-merge-submodule.sh
new file mode 100755
index 0000000000..d1e9fcc781
--- /dev/null
+++ b/t/t7613-merge-submodule.sh
@@ -0,0 +1,19 @@
+#!/bin/sh
+
+test_description='merge can handle submodules'
+
+. ./test-lib.sh
+. "$TEST_DIRECTORY"/lib-submodule-update.sh
+
+# merges without conflicts
+test_submodule_switch "git merge"
+
+test_submodule_switch "git merge --ff"
+
+test_submodule_switch "git merge --ff-only"
+
+KNOWN_FAILURE_NOFF_MERGE_DOESNT_CREATE_EMPTY_SUBMODULE_DIR=1
+KNOWN_FAILURE_NOFF_MERGE_ATTEMPTS_TO_MERGE_REMOVED_SUBMODULE_FILES=1
+test_submodule_switch "git merge --no-ff"
+
+test_done