diff --git a/cache-tree.c b/cache-tree.c
index 7881b42aa2..2b636eb3f8 100644
--- a/cache-tree.c
+++ b/cache-tree.c
@@ -238,8 +238,8 @@ int cache_tree_fully_valid(struct cache_tree *it)
 	if (!it)
 		return 0;
 	if (it->entry_count < 0 ||
-	    odb_has_object(the_repository->objects, &it->oid,
-			   ODB_HAS_OBJECT_RECHECK_PACKED | ODB_HAS_OBJECT_FETCH_PROMISOR))
+	    !odb_has_object(the_repository->objects, &it->oid,
+			    ODB_HAS_OBJECT_RECHECK_PACKED | ODB_HAS_OBJECT_FETCH_PROMISOR))
 		return 0;
 	for (i = 0; i < it->subtree_nr; i++) {
 		if (!cache_tree_fully_valid(it->down[i]->cache_tree))
diff --git a/t/t0090-cache-tree.sh b/t/t0090-cache-tree.sh
index d901588294..0964718d7f 100755
--- a/t/t0090-cache-tree.sh
+++ b/t/t0090-cache-tree.sh
@@ -278,4 +278,12 @@ test_expect_success 'switching trees does not invalidate shared index' '
 	)
 '
 
+test_expect_success 'cache-tree is used by write-tree when valid' '
+	test_commit use-valid &&
+
+	# write-tree with a valid cache-tree should skip cache_tree_update
+	GIT_TRACE2_PERF="$(pwd)/trace.output" git write-tree &&
+	test_grep ! region_enter.*cache_tree.*update trace.output
+'
+
 test_done