diff --git a/builtin/fsck.c b/builtin/fsck.c
index 821e7798c7..4d7f5c63ce 100644
--- a/builtin/fsck.c
+++ b/builtin/fsck.c
@@ -883,6 +883,8 @@ int cmd_fsck(int argc, const char **argv, const char *prefix)
 		verify_index_checksum = 1;
 		verify_ce_order = 1;
 		read_cache();
+		/* TODO: audit for interaction with sparse-index. */
+		ensure_full_index(&the_index);
 		for (i = 0; i < active_nr; i++) {
 			unsigned int mode;
 			struct blob *blob;