diff --git a/builtin/diff-index.c b/builtin/diff-index.c
index 3e05260ac0e040..685b60284fd9e7 100644
--- a/builtin/diff-index.c
+++ b/builtin/diff-index.c
@@ -25,6 +25,10 @@ int cmd_diff_index(int argc, const char **argv, const char *prefix)
 		usage(diff_cache_usage);
 
 	git_config(git_diff_basic_config, NULL); /* no "diff" UI options */
+
+	prepare_repo_settings(the_repository);
+	the_repository->settings.command_requires_full_index = 0;
+
 	repo_init_revisions(the_repository, &rev, prefix);
 	rev.abbrev = 0;
 	prefix = precompose_argv_prefix(argc, argv, prefix);
diff --git a/t/t1092-sparse-checkout-compatibility.sh b/t/t1092-sparse-checkout-compatibility.sh
index a2c0e1b4dcc564..6fa7f5e9587af8 100755
--- a/t/t1092-sparse-checkout-compatibility.sh
+++ b/t/t1092-sparse-checkout-compatibility.sh
@@ -803,6 +803,8 @@ test_expect_success 'update-index --remove outside sparse definition' '
 	test_sparse_match git diff --cached --name-status &&
 	test_cmp expect sparse-checkout-out &&
 
+	test_sparse_match git diff-index --cached HEAD &&
+
 	# Reset the state
 	test_all_match git reset --hard &&
 
@@ -812,6 +814,8 @@ test_expect_success 'update-index --remove outside sparse definition' '
 	test_sparse_match git diff --cached --name-status &&
 	test_must_be_empty sparse-checkout-out &&
 
+	test_sparse_match git diff-index --cached HEAD &&
+
 	# Reset the state
 	test_all_match git reset --hard &&
 
@@ -823,7 +827,9 @@ test_expect_success 'update-index --remove outside sparse definition' '
 	D	folder1/a
 	EOF
 	test_sparse_match git diff --cached --name-status &&
-	test_cmp expect sparse-checkout-out
+	test_cmp expect sparse-checkout-out &&
+
+	test_sparse_match git diff-index --cached HEAD
 '
 
 test_expect_success 'update-index with directories' '
@@ -1551,7 +1557,7 @@ test_expect_success 'sparse-index is not expanded: describe' '
 	ensure_not_expanded describe
 '
 
-test_expect_success 'sparse index is not expanded: diff' '
+test_expect_success 'sparse index is not expanded: diff and diff-index' '
 	init_repos &&
 
 	write_script edit-contents <<-\EOF &&
@@ -1568,6 +1574,7 @@ test_expect_success 'sparse index is not expanded: diff' '
 	test_all_match git diff --cached &&
 	ensure_not_expanded diff &&
 	ensure_not_expanded diff --cached &&
+	ensure_not_expanded diff-index --cached HEAD &&
 
 	# Add file outside cone
 	test_all_match git reset --hard &&
@@ -1582,6 +1589,7 @@ test_expect_success 'sparse index is not expanded: diff' '
 	test_all_match git diff --cached &&
 	ensure_not_expanded diff &&
 	ensure_not_expanded diff --cached &&
+	ensure_not_expanded diff-index --cached HEAD &&
 
 	# Merge conflict outside cone
 	# The sparse checkout will report a warning that is not in the
@@ -1594,7 +1602,8 @@ test_expect_success 'sparse index is not expanded: diff' '
 	test_all_match git diff &&
 	test_all_match git diff --cached &&
 	ensure_not_expanded diff &&
-	ensure_not_expanded diff --cached
+	ensure_not_expanded diff --cached &&
+	ensure_not_expanded diff-index --cached HEAD
 '
 
 test_expect_success 'sparse index is not expanded: show and rev-parse' '