diff --git a/src/racket/gc2/newgc.c b/src/racket/gc2/newgc.c
index 77d704a43c..9d871a4cf4 100644
--- a/src/racket/gc2/newgc.c
+++ b/src/racket/gc2/newgc.c
@@ -48,7 +48,6 @@ intptr_t mp_ac_freed;
 
 #if 0
 #define POINTER_OWNERSHIP_CHECK
-#define LOCK_PAGE_TABLES_FOR_DEBUG
 #endif
 
 #define MZ_PRECISE_GC /* required for mz includes to work right */
@@ -378,17 +377,67 @@ inline static void check_used_against_max(NewGC *gc, size_t len)
 
 #include "vm.c"
 
+#ifdef POINTER_OWNERSHIP_CHECK
+# define SHARED_PAGE_ORPHANED ((NewGC *)0x1)
+static mzrt_mutex *lock;
+static PageMap shared_pagemap;
+inline static void pagemap_set(PageMap page_maps1, void *p, mpage *value);
+inline static mpage *pagemap_find_page(PageMap page_maps1, const void *p);
+void shared_pagemap_set(void *ptr, size_t len, NewGC *owner)
+{
+  if (!lock) {
+    mzrt_mutex_create(&lock);
+# ifdef SIXTY_FOUR_BIT_INTEGERS
+    shared_pagemap = ofm_malloc_zero(PAGEMAP64_LEVEL1_SIZE * sizeof (mpage***)); 
+# else
+    shared_pagemap = ofm_malloc_zero(PAGEMAP32_SIZE * sizeof (mpage*)); 
+# endif
+  }
+
+  mzrt_mutex_lock(lock);
+  while (len > 0) {
+    pagemap_set(shared_pagemap, ptr, (mpage*)owner);
+    len -= APAGE_SIZE;
+    ptr = (char *)ptr + APAGE_SIZE;
+  }
+  mzrt_mutex_unlock(lock);
+}
+void check_page_owner(NewGC *gc, const void *p)
+{
+  NewGC *owner;
+  owner = (NewGC *)pagemap_find_page(shared_pagemap, p);
+  if (owner && (owner != gc) && (owner != MASTERGC) && (owner != SHARED_PAGE_ORPHANED)) {
+    mzrt_mutex_lock(lock);
+    owner = (NewGC *)pagemap_find_page(shared_pagemap, p);
+    if (owner && (owner != gc) && (owner != MASTERGC) && (owner != SHARED_PAGE_ORPHANED)) {
+      printf("%p is owned by place %i not the current place %i\n", p, owner->place_id, gc->place_id);  
+      abort();
+    }
+    mzrt_mutex_unlock(lock);
+  }
+}
+#endif
+
 static void *malloc_pages(NewGC *gc, size_t len, size_t alignment, int dirty, int type, int expect_mprotect, void **src_block)
 {
   void *ptr;
   check_used_against_max(gc, len);
   ptr = mmu_alloc_page(gc->mmu, len, alignment, dirty, type, expect_mprotect, src_block);
   if (!ptr) out_of_memory();
+
+#ifdef POINTER_OWNERSHIP_CHECK
+  shared_pagemap_set(ptr, len, gc);
+#endif
+
   return ptr;
 }
 
 static void free_pages(NewGC *gc, void *p, size_t len, int type, int expect_mprotect, void **src_block)
 {
+#ifdef POINTER_OWNERSHIP_CHECK
+  shared_pagemap_set(p, len, NULL);
+#endif
+
   gc->used_pages -= size_to_apage_count(len);
   mmu_free_page(gc->mmu, p, len, type, expect_mprotect, src_block, 1);
 }
@@ -403,6 +452,10 @@ static void check_excessive_free_pages(NewGC *gc) {
 }
 
 static void free_orphaned_page(NewGC *gc, mpage *tmp) {
+#ifdef POINTER_OWNERSHIP_CHECK
+  shared_pagemap_set(tmp->addr, round_to_apage_size(tmp->size), NULL);
+#endif
+
   /* free_pages decrements gc->used_pages which is incorrect, since this is an orphaned page,
    * so we use mmu_free_page directly */
   mmu_free_page(gc->mmu, tmp->addr, round_to_apage_size(tmp->size),
@@ -423,6 +476,11 @@ static void orphan_page_accounting(NewGC *gc, size_t allocate_size) {
 inline static void pagemap_add_with_size(PageMap pagemap, mpage *page, intptr_t size);
 static void adopt_page_accounting(NewGC *gc, mpage* tmp) {
   size_t realpagesize = real_page_size(tmp);
+
+#ifdef POINTER_OWNERSHIP_CHECK
+  shared_pagemap_set(tmp->addr, realpagesize, gc);
+#endif
+
   pagemap_add_with_size(gc->page_maps, tmp, realpagesize);
   mmu_memory_allocated_inc(gc->mmu, realpagesize);
   gc->used_pages += size_to_apage_count(realpagesize);
@@ -480,10 +538,6 @@ inline static void free_page_maps(PageMap page_maps1) {
 /* the page map makes a nice mapping from addresses to pages, allowing
    fairly fast lookup. this is useful. */
 inline static void pagemap_set(PageMap page_maps1, void *p, mpage *value) {
-#ifdef LOCK_PAGE_TABLES_FOR_DEBUG
-  NewGC *gc = GC_get_GC();
-  mzrt_mutex_lock(gc->pagetable_lock);
-#endif
 #ifdef SIXTY_FOUR_BIT_INTEGERS
   uintptr_t pos;
   mpage ***page_maps2;
@@ -505,34 +559,9 @@ inline static void pagemap_set(PageMap page_maps1, void *p, mpage *value) {
 #else
   page_maps1[PAGEMAP32_BITS(p)] = value;
 #endif
-#ifdef LOCK_PAGE_TABLES_FOR_DEBUG
-  mzrt_mutex_unlock(gc->pagetable_lock);
-#endif
 }
 
 inline static mpage *pagemap_find_page(PageMap page_maps1, const void *p) {
-#ifdef LOCK_PAGE_TABLES_FOR_DEBUG
-
-  mpage *result = NULL;
-  NewGC *gc = GC_get_GC();
-  mzrt_mutex_lock(gc->pagetable_lock);
-#ifdef SIXTY_FOUR_BIT_INTEGERS
-  mpage ***page_maps2;
-  mpage **page_maps3;
-
-  page_maps2 = page_maps1[PAGEMAP64_LEVEL1_BITS(p)];
-  if (!page_maps2) goto done;
-  page_maps3 = page_maps2[PAGEMAP64_LEVEL2_BITS(p)];
-  if (!page_maps3) goto done;
-  result = page_maps3[PAGEMAP64_LEVEL3_BITS(p)];
- done:
-#else
-  result = page_maps1[PAGEMAP32_BITS(p)];
-#endif
-  mzrt_mutex_unlock(gc->pagetable_lock);
-  return result;
-#else
-
 #ifdef SIXTY_FOUR_BIT_INTEGERS
   mpage ***page_maps2;
   mpage **page_maps3;
@@ -545,8 +574,6 @@ inline static mpage *pagemap_find_page(PageMap page_maps1, const void *p) {
 #else
   return page_maps1[PAGEMAP32_BITS(p)];
 #endif
-
-#endif
 }
 
 #if 0
@@ -958,6 +985,9 @@ static void *allocate_big(const size_t request_size_bytes, int type)
        page is going to be sent to a different place, so don't account
        for it here, and don't put it in the page_map */
     orphan_page_accounting(gc, allocate_size);
+#ifdef POINTER_OWNERSHIP_CHECK
+    shared_pagemap_set(bpage->addr, round_to_apage_size(allocate_size), SHARED_PAGE_ORPHANED);
+#endif
   } else
     pagemap_add(gc->page_maps, bpage);
   
@@ -994,9 +1024,12 @@ inline static mpage *create_new_medium_page(NewGC *gc, const int sz, const int p
   gc->med_pages[pos] = page;
   gc->med_freelist_pages[pos] = page;
 
-  if (gc->saved_allocator) /* see MESSAGE ALLOCATION above */
+  if (gc->saved_allocator) { /* see MESSAGE ALLOCATION above */
     orphan_page_accounting(gc, APAGE_SIZE);
-  else
+#ifdef POINTER_OWNERSHIP_CHECK
+    shared_pagemap_set(page->addr, APAGE_SIZE, SHARED_PAGE_ORPHANED);
+#endif    
+  } else
     pagemap_add(gc->page_maps, page);
 
   return page;
@@ -1105,9 +1138,12 @@ inline static mpage *gen0_create_new_nursery_mpage(NewGC *gc, const size_t page_
   page->size = PREFIX_SIZE;
   GEN0_ALLOC_SIZE(page) = page_size;
 
-  if (gc->saved_allocator)  /* see MESSAGE ALLOCATION above */
+  if (gc->saved_allocator) { /* see MESSAGE ALLOCATION above */
     orphan_page_accounting(gc, page_size);
-  else
+#ifdef POINTER_OWNERSHIP_CHECK
+    shared_pagemap_set(page->addr, page_size, SHARED_PAGE_ORPHANED);
+#endif    
+  } else
     pagemap_add_with_size(gc->page_maps, page, page_size);
 
   GCVERBOSEPAGE(gc, "NEW gen0", page);
@@ -2417,9 +2453,6 @@ static void NewGCMasterInfo_initialize() {
   MASTERGCINFO->alive = 0;
   MASTERGCINFO->ready = 0;
   MASTERGCINFO->signal_fds = realloc(MASTERGCINFO->signal_fds, sizeof(void*) * MASTERGCINFO->size);
-#ifdef POINTER_OWNERSHIP_CHECK
-  MASTERGCINFO->places_gcs = ofm_malloc_zero(sizeof(NewGC*) * MASTERGCINFO->size);
-#endif
   for (i=0; i < 32; i++ ) {
     MASTERGCINFO->signal_fds[i] = (void *)REAPED_SLOT_AVAILABLE;
   }
@@ -2564,9 +2597,6 @@ static intptr_t NewGCMasterInfo_find_free_id() {
     MASTERGCINFO->size++;
     MASTERGCINFO->alive++;
     MASTERGCINFO->signal_fds = realloc(MASTERGCINFO->signal_fds, sizeof(void*) * MASTERGCINFO->size);
-#ifdef POINTER_OWNERSHIP_CHECK
-    MASTERGCINFO->places_gcs= realloc(MASTERGCINFO->places_gcs, sizeof(NewGC*) * MASTERGCINFO->size);
-#endif
     return MASTERGCINFO->size - 1;
   }
   else {
@@ -2590,9 +2620,6 @@ static void NewGCMasterInfo_register_gc(NewGC *newgc) {
     intptr_t newid = NewGCMasterInfo_find_free_id();
     newgc->place_id = newid;
     MASTERGCINFO->signal_fds[newid] = (void *) CREATED_BUT_NOT_REGISTERED;
-#ifdef POINTER_OWNERSHIP_CHECK
-    MASTERGCINFO->places_gcs[newid] = newgc;
-#endif
   }
   GC_LOCK_DEBUG("UNMGCLOCK NewGCMasterInfo_register_gc\n");
   mzrt_rwlock_unlock(MASTERGCINFO->cangc);
@@ -2665,9 +2692,6 @@ static NewGC *init_type_tags_worker(NewGC *inheritgc, NewGC *parentgc,
   NewGC *gc;
 
   gc = ofm_malloc_zero(sizeof(NewGC));
-#ifdef LOCK_PAGE_TABLES_FOR_DEBUG
-  mzrt_mutex_create(&gc->pagetable_lock);
-#endif
 
   /* NOTE sets the constructed GC as the new Thread Specific GC. */
   GC_set_GC(gc);
@@ -2742,9 +2766,6 @@ void GC_destruct_child_gc() {
     waiting = MASTERGC->major_places_gc;
     if (!waiting) {
       MASTERGCINFO->signal_fds[gc->place_id] = (void *) REAPED_SLOT_AVAILABLE;
-#ifdef POINTER_OWNERSHIP_CHECK
-      MASTERGCINFO->places_gcs[gc->place_id] = NULL;
-#endif
       gc->place_id = -1;
       MASTERGCINFO->alive--;
     }
@@ -2964,23 +2985,7 @@ void GC_mark2(const void *const_p, struct NewGC *gc)
 #endif
       {
 #ifdef POINTER_OWNERSHIP_CHECK
-        mzrt_rwlock_wrlock(MASTERGCINFO->cangc);
-        {
-          int i;
-          int size = MASTERGCINFO->size;
-          for (i = 1; i < size; i++) {
-            if (gc->place_id != i 
-                && MASTERGCINFO->signal_fds[i] != (void*) REAPED_SLOT_AVAILABLE
-                && MASTERGCINFO->signal_fds[i] != (void*) CREATED_BUT_NOT_REGISTERED
-                && MASTERGCINFO->signal_fds[i] != (void*) SIGNALED_BUT_NOT_REGISTERED) {
-              if((page = pagemap_find_page(MASTERGCINFO->places_gcs[i]->page_maps, p))) {
-                printf("%p is owned by place %i not the current place %i\n", p, i, gc->place_id);  
-                asm("int3");
-              }
-            }
-          }
-        }
-        mzrt_rwlock_unlock(MASTERGCINFO->cangc);
+        check_page_owner(gc, p);
 #endif
         GCDEBUG((DEBUGOUTF,"Not marking %p (no page)\n",p));
         return;
@@ -3319,7 +3324,12 @@ void GC_fixup2(void *pp, struct NewGC *gc)
     if(info->mark && info->moved) 
       *(void**)pp = *(void**)p;
     else GCDEBUG((DEBUGOUTF, "Not repairing %p from %p (not moved)\n",p,pp));
-  } else GCDEBUG((DEBUGOUTF, "Not repairing %p from %p (no page)\n", p, pp));
+  } else {
+#ifdef POINTER_OWNERSHIP_CHECK
+    check_page_owner(gc, p);
+#endif
+    GCDEBUG((DEBUGOUTF, "Not repairing %p from %p (no page)\n", p, pp));
+  }
 }
 
 void GC_fixup(void *pp)
diff --git a/src/racket/gc2/newgc.h b/src/racket/gc2/newgc.h
index 04a47f45d0..1afef913b3 100644
--- a/src/racket/gc2/newgc.h
+++ b/src/racket/gc2/newgc.h
@@ -119,9 +119,6 @@ typedef struct NewGCMasterInfo {
   uintptr_t alive;
   uintptr_t ready;
   void **signal_fds;
-#ifdef POINTER_OWNERSHIP_CHECK
-  struct NewGC **places_gcs;
-#endif
   mzrt_rwlock *cangc;
   mzrt_sema *wait_sema;
 } NewGCMasterInfo;
@@ -140,9 +137,6 @@ typedef struct NewGC {
   Mark2_Proc  *mark_table;   /* the table of mark procs */
   Fixup2_Proc *fixup_table;  /* the table of repair procs */
   PageMap page_maps;
-#ifdef LOCK_PAGE_TABLES_FOR_DEBUG
-  mzrt_mutex *pagetable_lock;
-#endif
 
   /* All non-gen0 pages are held in the following structure. */
   struct mpage *gen1_pages[PAGE_TYPES];