diff --git a/mps/code/cbs.c b/mps/code/cbs.c
index 73474a02de9..6eff37a844e 100644
--- a/mps/code/cbs.c
+++ b/mps/code/cbs.c
@@ -194,36 +194,32 @@ static Compare cbsSplayCompare(void *key, SplayNode node)
 /* cbsTestNode, cbsTestTree -- test for nodes larger than the S parameter */
 
 static Bool cbsTestNode(SplayTree tree, SplayNode node,
-                        void *closureP, unsigned long closureS)
+                        void *closureP, Size size)
 {
-  Size size;
   CBSBlock block;
 
   AVERT(SplayTree, tree);
   AVERT(SplayNode, node);
   AVER(closureP == NULL);
-  AVER(closureS > 0);
+  AVER(size > 0);
   AVER(cbsOfSplayTree(tree)->fastFind);
 
-  size = (Size)closureS;
   block = cbsBlockOfSplayNode(node);
 
   return CBSBlockSize(block) >= size;
 }
 
 static Bool cbsTestTree(SplayTree tree, SplayNode node,
-                        void *closureP, unsigned long closureS)
+                        void *closureP, Size size)
 {
-  Size size;
   CBSBlock block;
 
   AVERT(SplayTree, tree);
   AVERT(SplayNode, node);
   AVER(closureP == NULL);
-  AVER(closureS > 0);
+  AVER(size > 0);
   AVER(cbsOfSplayTree(tree)->fastFind);
 
-  size = (Size)closureS;
   block = cbsBlockOfSplayNode(node);
 
   return block->maxSize >= size;
@@ -1396,7 +1392,7 @@ Bool CBSFindFirst(Addr *baseReturn, Addr *limitReturn,
 
     METER_ACC(cbs->splaySearch, cbs->splayTreeSize);
     found = SplayFindFirst(&node, splayTreeOfCBS(cbs), &cbsTestNode,
-                           &cbsTestTree, NULL, (unsigned long)size);
+                           &cbsTestTree, NULL, size);
 
     if (found) {
       CBSBlock block;
@@ -1479,7 +1475,7 @@ Bool CBSFindLast(Addr *baseReturn, Addr *limitReturn,
 
     METER_ACC(cbs->splaySearch, cbs->splayTreeSize);
     found = SplayFindLast(&node, splayTreeOfCBS(cbs), &cbsTestNode,
-                          &cbsTestTree, NULL, (unsigned long)size);
+                          &cbsTestTree, NULL, size);
     if (found) {
       CBSBlock block;
 
@@ -1573,7 +1569,7 @@ Bool CBSFindLargest(Addr *baseReturn, Addr *limitReturn,
       size = cbsBlockOfSplayNode(root)->maxSize;
       METER_ACC(cbs->splaySearch, cbs->splayTreeSize);
       found = SplayFindFirst(&node, splayTreeOfCBS(cbs), &cbsTestNode,
-                             &cbsTestTree, NULL, (unsigned long)size);
+                             &cbsTestTree, NULL, size);
       AVER(found); /* maxSize is exact, so we will find it. */
       block = cbsBlockOfSplayNode(node);
       AVER(CBSBlockSize(block) >= size);
diff --git a/mps/code/splay.c b/mps/code/splay.c
index 7979af342c4..4668a23e48a 100644
--- a/mps/code/splay.c
+++ b/mps/code/splay.c
@@ -883,7 +883,7 @@ static Compare SplayFindLastCompare(void *key, SplayNode node)
 Bool SplayFindFirst(SplayNode *nodeReturn, SplayTree tree,
                            SplayTestNodeMethod testNode,
                            SplayTestTreeMethod testTree,
-                           void *closureP, unsigned long closureS)
+                           void *closureP, Size closureS)
 {
   SplayNode node;
   SplayFindClosureStruct closureStruct;
@@ -919,7 +919,7 @@ Bool SplayFindFirst(SplayNode *nodeReturn, SplayTree tree,
 Bool SplayFindLast(SplayNode *nodeReturn, SplayTree tree,
                           SplayTestNodeMethod testNode,
                           SplayTestTreeMethod testTree,
-                          void *closureP, unsigned long closureS)
+                          void *closureP, Size closureS)
 {
   SplayNode node;
   SplayFindClosureStruct closureStruct;
diff --git a/mps/code/splay.h b/mps/code/splay.h
index bdb4d888f87..8fa31af7fd3 100644
--- a/mps/code/splay.h
+++ b/mps/code/splay.h
@@ -17,9 +17,9 @@ typedef struct SplayNodeStruct *SplayNode;
 typedef unsigned Compare;
 typedef Compare (*SplayCompareMethod)(void *key, SplayNode node);
 typedef Bool (*SplayTestNodeMethod)(SplayTree tree, SplayNode node,
-                                    void *closureP, unsigned long closureS);
+                                    void *closureP, Size closureS);
 typedef Bool (*SplayTestTreeMethod)(SplayTree tree, SplayNode node,
-                                    void *closureP, unsigned long closureS);
+                                    void *closureP, Size closureS);
 typedef void (*SplayUpdateNodeMethod)(SplayTree tree, SplayNode node,
                                       SplayNode leftChild,
                                       SplayNode rightChild);
@@ -67,11 +67,11 @@ extern SplayNode SplayTreeNext(SplayTree tree, SplayNode oldNode,
 extern Bool SplayFindFirst(SplayNode *nodeReturn, SplayTree tree,
                            SplayTestNodeMethod testNode,
                            SplayTestTreeMethod testTree,
-                           void *closureP, unsigned long closureS);
+                           void *closureP, Size closureS);
 extern Bool SplayFindLast(SplayNode *nodeReturn, SplayTree tree,
                           SplayTestNodeMethod testNode,
                           SplayTestTreeMethod testTree,
-                          void *closureP, unsigned long closureS);
+                          void *closureP, Size closureS);
 
 extern void SplayNodeRefresh(SplayTree tree, SplayNode node, void *key);