diff --git a/mps/code/mpsi.c b/mps/code/mpsi.c
index 942bf7a0021..c00da18c201 100644
--- a/mps/code/mpsi.c
+++ b/mps/code/mpsi.c
@@ -928,7 +928,7 @@ mps_bool_t (mps_commit)(mps_ap_t mps_ap, mps_addr_t p, size_t size)
   AVER(p != NULL);
   AVER(size > 0);
   AVER(p == mps_ap->init);
-  AVER((void *)((char *)mps_ap->init + size) == mps_ap->alloc);
+  AVER(PointerAdd(mps_ap->init, size) == mps_ap->alloc);
 
   return mps_commit(mps_ap, p, size);
 }