diff --git a/btree.h b/btree.h
index c7a977a..0abe101 100644
--- a/btree.h
+++ b/btree.h
@@ -574,9 +574,9 @@ class btree_node {
   btree_node* child(int i) const { return fields_.children[i]; }
   btree_node** mutable_child(int i) { return &fields_.children[i]; }
   void set_child(int i, btree_node *c) {
-    *mutable_child(i) = c;
-    c->fields_.parent = this;
-    c->fields_.position = i;
+    reinterpret_cast<internal_fields*>(this)->children[i] = c;
+    reinterpret_cast<internal_fields*>(c)->parent = this;
+    reinterpret_cast<internal_fields*>(c)->position = i;
   }
 
   // Returns the position of the first value whose key is not less than k.