diff --git a/runtime/gc/dfs-mark.c b/runtime/gc/dfs-mark.c
index 95d0e706c..bf7a1b95e 100644
--- a/runtime/gc/dfs-mark.c
+++ b/runtime/gc/dfs-mark.c
@@ -140,7 +140,7 @@ size_t dfsMarkByMode (GC_state s, pointer root,
     assert (objptrIndex < numObjptrs);
     // next = *(pointer*)todo;
     next = fetchObjptrToPointer (todo, s->heap.start);
-    if (not isPointer (next)) {
+    if (not isPointerInHeap (s, next)) {
 markNextInNormal:
       assert (objptrIndex < numObjptrs);
       objptrIndex++;
@@ -170,7 +170,7 @@ size_t dfsMarkByMode (GC_state s, pointer root,
       if (DEBUG_WEAK)
         fprintf (stderr, "marking weak "FMTPTR" ",
                  (uintptr_t)w);
-      if (isObjptr (w->objptr)) {
+      if (isObjptrInHeap (s, w->objptr)) {
         if (DEBUG_WEAK)
           fprintf (stderr, "linking\n");
         w->link = s->weaks;
@@ -216,7 +216,7 @@ size_t dfsMarkByMode (GC_state s, pointer root,
     assert (todo == indexSequenceAtObjptrIndex (s, cur, sequenceIndex, objptrIndex));
     // next = *(pointer*)todo;
     next = fetchObjptrToPointer (todo, s->heap.start);
-    if (not (isPointer(next))) {
+    if (not (isPointerInHeap(s, next))) {
 markNextInSequence:
       assert (sequenceIndex < getSequenceLength (cur));
       assert (objptrIndex < numObjptrs);
@@ -279,7 +279,7 @@ size_t dfsMarkByMode (GC_state s, pointer root,
                "    offset %u  todo "FMTPTR"  next = "FMTPTR"\n",
                frameOffsets [objptrIndex + 1],
                (uintptr_t)todo, (uintptr_t)next);
-    if (not isPointer (next)) {
+    if (not isPointerInHeap (s, next)) {
       objptrIndex++;
       goto markInFrame;
     }
diff --git a/runtime/gc/heap.h b/runtime/gc/heap.h
index e0fe7bc15..a454885c3 100644
--- a/runtime/gc/heap.h
+++ b/runtime/gc/heap.h
@@ -39,13 +39,11 @@ typedef struct GC_heap {
 
 static inline bool isPointerInOldGen (GC_state s, pointer p);
 static inline bool isPointerInNursery (GC_state s, pointer p);
-#if ASSERT
+static inline bool isPointerInHeap (GC_state s, pointer p);
 static inline bool isObjptrInOldGen (GC_state s, objptr op);
-#endif
 static inline bool isObjptrInNursery (GC_state s, objptr op);
-#if ASSERT
 static inline bool isObjptrInFromSpace (GC_state s, objptr op);
-#endif
+static inline bool isObjptrInHeap (GC_state s, objptr op);
 static inline bool hasHeapBytesFree (GC_state s, size_t oldGen, size_t nursery);
 static inline bool isHeapInit (GC_heap h);
 
diff --git a/runtime/gc/heap_predicates.c b/runtime/gc/heap_predicates.c
index bb279aab9..dfbfb5a6c 100644
--- a/runtime/gc/heap_predicates.c
+++ b/runtime/gc/heap_predicates.c
@@ -18,7 +18,6 @@ bool isPointerInNursery (GC_state s, pointer p) {
               and p <= s->frontier));
 }
 
-#if ASSERT
 bool isObjptrInOldGen (GC_state s, objptr op) {
   pointer p;
   if (not (isObjptr(op)))
@@ -26,7 +25,6 @@ bool isObjptrInOldGen (GC_state s, objptr op) {
   p = objptrToPointer (op, s->heap.start);
   return isPointerInOldGen (s, p);
 }
-#endif
 
 bool isObjptrInNursery (GC_state s, objptr op) {
   pointer p;
@@ -36,12 +34,19 @@ bool isObjptrInNursery (GC_state s, objptr op) {
   return isPointerInNursery (s, p);
 }
 
-#if ASSERT
 bool isObjptrInFromSpace (GC_state s, objptr op) {
   return (isObjptrInOldGen (s, op) 
           or isObjptrInNursery (s, op));
 }
-#endif
+
+bool isObjptrInHeap (GC_state s, objptr op) {
+  return isObjptrInFromSpace(s, op);
+}
+
+bool isPointerInHeap (GC_state s, pointer p) {
+  return (isPointerInOldGen (s, p)
+          or isPointerInNursery (s, p));
+}
 
 bool hasHeapBytesFree (GC_state s, size_t oldGen, size_t nursery) {
   size_t total;