diff --git a/builtin/diff.c b/builtin/diff.c
index dd8ce688ba7054..cbf7b51c7c0ece 100644
--- a/builtin/diff.c
+++ b/builtin/diff.c
@@ -437,6 +437,9 @@ int cmd_diff(int argc, const char **argv, const char *prefix)
 
 	prefix = setup_git_directory_gently(&nongit);
 
+	prepare_repo_settings(the_repository);
+	the_repository->settings.command_requires_full_index = 0;
+
 	if (!no_index) {
 		/*
 		 * Treat git diff with at least one path outside of the
diff --git a/t/t1092-sparse-checkout-compatibility.sh b/t/t1092-sparse-checkout-compatibility.sh
index 3e24c00140e810..40474322414566 100755
--- a/t/t1092-sparse-checkout-compatibility.sh
+++ b/t/t1092-sparse-checkout-compatibility.sh
@@ -417,6 +417,43 @@ test_expect_success 'diff --staged' '
 	test_all_match git diff --staged
 '
 
+test_expect_success 'diff partially-staged' '
+	init_repos &&
+
+	write_script edit-contents <<-\EOF &&
+	echo text >>$1
+	EOF
+
+	# Add file within cone
+	test_all_match git sparse-checkout set deep &&
+	run_on_all ../edit-contents deep/testfile &&
+	test_all_match git add deep/testfile &&
+	run_on_all ../edit-contents deep/testfile &&
+
+	test_all_match git diff &&
+	test_all_match git diff --staged &&
+
+	# Add file outside cone
+	test_all_match git reset --hard &&
+	run_on_all mkdir newdirectory &&
+	run_on_all ../edit-contents newdirectory/testfile &&
+	test_all_match git sparse-checkout set newdirectory &&
+	test_all_match git add newdirectory/testfile &&
+	run_on_all ../edit-contents newdirectory/testfile &&
+	test_all_match git sparse-checkout set &&
+
+	test_all_match git diff &&
+	test_all_match git diff --staged &&
+
+	# Merge conflict outside cone
+	test_all_match git reset --hard &&
+	test_all_match git checkout merge-left &&
+	test_all_match test_must_fail git merge merge-right &&
+
+	test_all_match git diff &&
+	test_all_match git diff --staged
+'
+
 # NEEDSWORK: sparse-checkout behaves differently from full-checkout when
 # running this test with 'df-conflict-2' after 'df-conflict-1'.
 test_expect_success 'diff with renames and conflicts' '
@@ -872,6 +909,11 @@ test_expect_success 'sparse-index is not expanded' '
 
 	ensure_not_expanded reset --hard update-deep &&
 
+	echo a test change >>sparse-index/README.md &&
+	ensure_not_expanded diff &&
+	git -C sparse-index add README.md &&
+	ensure_not_expanded diff --staged &&
+
 	ensure_not_expanded reset base -- deep/a &&
 	ensure_not_expanded reset base -- nonexistent-file &&
 	ensure_not_expanded reset deepest -- deep &&