diff --git a/include/mimalloc-internal.h b/include/mimalloc-internal.h
index 97abb4a..14c111c 100644
--- a/include/mimalloc-internal.h
+++ b/include/mimalloc-internal.h
@@ -59,7 +59,7 @@ void       _mi_page_abandon(mi_page_t* page, mi_page_queue_t* pq);            //
 void       _mi_heap_delayed_free(mi_heap_t* heap);
 
 void       _mi_page_use_delayed_free(mi_page_t* page, bool enable);
-void       _mi_page_queue_append(mi_heap_t* heap, mi_page_queue_t* pq, mi_page_queue_t* append);
+size_t     _mi_page_queue_append(mi_heap_t* heap, mi_page_queue_t* pq, mi_page_queue_t* append);
 void       _mi_deferred_free(mi_heap_t* heap, bool force);
 
 void       _mi_page_free_collect(mi_page_t* page);
@@ -136,6 +136,7 @@ static inline bool mi_mul_overflow(size_t size, size_t count, size_t* total) {
 // Align a byte size to a size in _machine words_,
 // i.e. byte size == `wsize*sizeof(void*)`.
 static inline size_t _mi_wsize_from_size(size_t size) {
+  mi_assert_internal(size <= SIZE_MAX - sizeof(uintptr_t));
   return (size + sizeof(uintptr_t) - 1) / sizeof(uintptr_t);
 }
 
@@ -190,7 +191,7 @@ static inline mi_segment_t* _mi_ptr_segment(const void* p) {
 // Segment belonging to a page
 static inline mi_segment_t* _mi_page_segment(const mi_page_t* page) {
   mi_segment_t* segment = _mi_ptr_segment(page);
-  mi_assert_internal(page == &segment->pages[page->segment_idx]);
+  mi_assert_internal(segment == NULL || page == &segment->pages[page->segment_idx]);
   return segment;
 }
 
diff --git a/src/heap.c b/src/heap.c
index f474b1a..57cb4f7 100644
--- a/src/heap.c
+++ b/src/heap.c
@@ -302,9 +302,12 @@ static void mi_heap_absorb(mi_heap_t* heap, mi_heap_t* from) {
   for (size_t i = 0; i < MI_BIN_FULL; i++) {
     mi_page_queue_t* pq = &heap->pages[i];
     mi_page_queue_t* append = &from->pages[i];
-    _mi_page_queue_append(heap, pq, append);
+    size_t pcount = _mi_page_queue_append(heap, pq, append);
+    heap->page_count += pcount;
+    from->page_count -= pcount;
   }
   mi_assert_internal(from->thread_delayed_free == NULL);
+  mi_assert_internal(from->page_count == 0);
   
   // and reset the `from` heap
   mi_heap_reset_pages(from);
diff --git a/src/page-queue.c b/src/page-queue.c
index 4d3547a..ba5e929 100644
--- a/src/page-queue.c
+++ b/src/page-queue.c
@@ -323,15 +323,17 @@ static void mi_page_queue_enqueue_from(mi_page_queue_t* to, mi_page_queue_t* fro
   page->flags.in_full = mi_page_queue_is_full(to);
 }
 
-void _mi_page_queue_append(mi_heap_t* heap, mi_page_queue_t* pq, mi_page_queue_t* append) {
+size_t _mi_page_queue_append(mi_heap_t* heap, mi_page_queue_t* pq, mi_page_queue_t* append) {
   mi_assert_internal(mi_heap_contains_queue(heap,pq));
   mi_assert_internal(pq->block_size == append->block_size);
 
-  if (append->first==NULL) return;
+  if (append->first==NULL) return 0;
 
-  // set append pages to new heap
+  // set append pages to new heap and count
+  size_t count = 0;
   for (mi_page_t* page = append->first; page != NULL; page = page->next) {
     page->heap = heap;
+    count++;
   }
 
   if (pq->last==NULL) {
@@ -349,4 +351,5 @@ void _mi_page_queue_append(mi_heap_t* heap, mi_page_queue_t* pq, mi_page_queue_t
     append->first->prev = pq->last;
     pq->last = append->last;
   }
+  return count;
 }