diff --git a/src/tree_schema.c b/src/tree_schema.c
index 18096a6..a99c8e5 100644
--- a/src/tree_schema.c
+++ b/src/tree_schema.c
@@ -998,6 +998,7 @@
     }
 
 cleanup:
+    assert(ret || main_set->objs);
     ly_set_free(dep_set, NULL);
     ly_set_free(ctx_set, NULL);
     return ret;