diff --git a/mps/code/sa.c b/mps/code/sa.c
index 0c1d951af5d..801a2523f55 100644
--- a/mps/code/sa.c
+++ b/mps/code/sa.c
@@ -25,8 +25,8 @@ void SparseArrayInit(SparseArray sa,
   sa->mapped = mapped;
   sa->pages = pages;
   sa->vm = vm;
-  AVER(SizeIsP2(VMPageSize(sa->vm)));
-  sa->shift = SizeLog2(VMPageSize(sa->vm));
+  AVER(SizeIsP2(VMPageSize(vm)));
+  sa->shift = SizeLog2(VMPageSize(vm));
   BTResRange(mapped, 0, length);
   BTResRange(pages, 0, pagesLength(sa));
 
diff --git a/mps/code/sa.h b/mps/code/sa.h
index cb889c988bb..1c742a49289 100644
--- a/mps/code/sa.h
+++ b/mps/code/sa.h
@@ -31,7 +31,7 @@ typedef struct SparseArrayStruct {
   BT mapped;            /* whether elements exist in the array */
   BT pages;             /* whether underlying pages are mapped */
   VM vm;                /* where pages are mapped from */
-  Shift shift;          /* SizeLog2(VMPageSize(sa->vm)) */
+  Shift shift;          /* SizeLog2(VMPageSize(vm)) TODO: VMShift(vm) */
 } SparseArrayStruct;
 
 extern void SparseArrayInit(SparseArray sa,