diff --git a/builtin/commit.c b/builtin/commit.c
index 985a0445b7..d7ccfa0bfa 100644
--- a/builtin/commit.c
+++ b/builtin/commit.c
@@ -991,11 +991,8 @@ static int prepare_to_commit(const char *index_file, const char *prefix,
 		struct object_id oid;
 		const char *parent = "HEAD";
 
-		if (!the_index.cache_nr) {
-			discard_index(&the_index);
-			if (repo_read_index(the_repository) < 0)
-				die(_("Cannot read index"));
-		}
+		if (!the_index.initialized && repo_read_index(the_repository) < 0)
+			die(_("Cannot read index"));
 
 		if (amend)
 			parent = "HEAD^1";
diff --git a/t/t2200-add-update.sh b/t/t2200-add-update.sh
index be394f1131..c01492f33f 100755
--- a/t/t2200-add-update.sh
+++ b/t/t2200-add-update.sh
@@ -197,4 +197,15 @@ test_expect_success '"add -u non-existent" should fail' '
 	! grep "non-existent" actual
 '
 
+test_expect_success '"commit -a" implies "add -u" if index becomes empty' '
+	git rm -rf \* &&
+	git commit -m clean-slate &&
+	test_commit file1 &&
+	rm file1.t &&
+	test_tick &&
+	git commit -a -m remove &&
+	git ls-tree HEAD: >out &&
+	test_must_be_empty out
+'
+
 test_done