diff --git a/t/helper/test-read-cache.c b/t/helper/test-read-cache.c
index 6cfd8f2de7..b52c174acc 100644
--- a/t/helper/test-read-cache.c
+++ b/t/helper/test-read-cache.c
@@ -4,6 +4,7 @@
 #include "blob.h"
 #include "commit.h"
 #include "tree.h"
+#include "sparse-index.h"
 
 static void print_cache_entry(struct cache_entry *ce)
 {
@@ -35,13 +36,19 @@ int cmd__read_cache(int argc, const char **argv)
 	struct repository *r = the_repository;
 	int i, cnt = 1;
 	const char *name = NULL;
-	int table = 0;
+	int table = 0, expand = 0;
+
+	initialize_the_repository();
+	prepare_repo_settings(r);
+	r->settings.command_requires_full_index = 0;
 
 	for (++argv, --argc; *argv && starts_with(*argv, "--"); ++argv, --argc) {
 		if (skip_prefix(*argv, "--print-and-refresh=", &name))
 			continue;
 		if (!strcmp(*argv, "--table"))
 			table = 1;
+		else if (!strcmp(*argv, "--expand"))
+			expand = 1;
 	}
 
 	if (argc == 1)
@@ -51,6 +58,10 @@ int cmd__read_cache(int argc, const char **argv)
 
 	for (i = 0; i < cnt; i++) {
 		repo_read_index(r);
+
+		if (expand)
+			ensure_full_index(r->index);
+
 		if (name) {
 			int pos;
 
diff --git a/t/t1092-sparse-checkout-compatibility.sh b/t/t1092-sparse-checkout-compatibility.sh
index de5d8461c9..a1aea141c6 100755
--- a/t/t1092-sparse-checkout-compatibility.sh
+++ b/t/t1092-sparse-checkout-compatibility.sh
@@ -130,6 +130,11 @@ test_sparse_match () {
 	test_cmp sparse-checkout-err sparse-index-err
 }
 
+test_expect_success 'expanded in-memory index matches full index' '
+	init_repos &&
+	test_sparse_match test-tool read-cache --expand --table
+'
+
 test_expect_success 'status with options' '
 	init_repos &&
 	test_all_match git status --porcelain=v2 &&