diff --git a/sparse-index.c b/sparse-index.c
index ef53bd2198b479..53c8f711ccc82e 100644
--- a/sparse-index.c
+++ b/sparse-index.c
@@ -186,6 +186,10 @@ int convert_to_sparse(struct index_state *istate)
 	cache_tree_free(&istate->cache_tree);
 	cache_tree_update(istate, 0);
 
+	istate->fsmonitor_has_run_once = 0;
+	FREE_AND_NULL(istate->fsmonitor_dirty);
+	FREE_AND_NULL(istate->fsmonitor_last_update);
+
 	istate->sparse_index = 1;
 	trace2_region_leave("index", "convert_to_sparse", istate->repo);
 	return 0;
@@ -282,6 +286,9 @@ void ensure_full_index(struct index_state *istate)
 	istate->cache = full->cache;
 	istate->cache_nr = full->cache_nr;
 	istate->cache_alloc = full->cache_alloc;
+	istate->fsmonitor_has_run_once = 0;
+	FREE_AND_NULL(istate->fsmonitor_dirty);
+	FREE_AND_NULL(istate->fsmonitor_last_update);
 
 	strbuf_release(&base);
 	free(full);
diff --git a/t/t7519-status-fsmonitor.sh b/t/t7519-status-fsmonitor.sh
index 637391c6ce4608..8f9240b9b1afad 100755
--- a/t/t7519-status-fsmonitor.sh
+++ b/t/t7519-status-fsmonitor.sh
@@ -73,6 +73,7 @@ test_expect_success 'setup' '
 	expect*
 	actual*
 	marker*
+	trace2*
 	EOF
 '
 
@@ -383,4 +384,51 @@ test_expect_success 'status succeeds after staging/unstaging' '
 	)
 '
 
+# Usage:
+# check_sparse_index_behavior [!]
+# If "!" is supplied, then we verify that we do not call ensure_full_index
+# during a call to 'git status'. Otherwise, we verify that we _do_ call it.
+check_sparse_index_behavior () {
+	git status --porcelain=v2 >expect &&
+	git sparse-checkout init --cone --sparse-index &&
+	git sparse-checkout set dir1 dir2 &&
+	GIT_TRACE2_EVENT="$(pwd)/trace2.txt" GIT_TRACE2_EVENT_NESTING=10 \
+		git status --porcelain=v2 >actual &&
+	test_region $1 index ensure_full_index trace2.txt &&
+	test_cmp expect actual &&
+	rm trace2.txt &&
+	git sparse-checkout disable
+}
+
+test_expect_success 'status succeeds with sparse index' '
+	git reset --hard &&
+
+	test_config core.fsmonitor "$TEST_DIRECTORY/t7519/fsmonitor-all" &&
+	check_sparse_index_behavior ! &&
+
+	write_script .git/hooks/fsmonitor-test<<-\EOF &&
+		printf "last_update_token\0"
+	EOF
+	git config core.fsmonitor .git/hooks/fsmonitor-test &&
+	check_sparse_index_behavior ! &&
+
+	write_script .git/hooks/fsmonitor-test<<-\EOF &&
+		printf "last_update_token\0"
+		printf "dir1/modified\0"
+	EOF
+	check_sparse_index_behavior ! &&
+
+	cp -r dir1 dir1a &&
+	git add dir1a &&
+	git commit -m "add dir1a" &&
+
+	# This one modifies outside the sparse-checkout definition
+	# and hence we expect to expand the sparse-index.
+	write_script .git/hooks/fsmonitor-test<<-\EOF &&
+		printf "last_update_token\0"
+		printf "dir1a/modified\0"
+	EOF
+	check_sparse_index_behavior
+'
+
 test_done