diff --git a/include/mimalloc/types.h b/include/mimalloc/types.h
index 9851ef5e..6727a87c 100644
--- a/include/mimalloc/types.h
+++ b/include/mimalloc/types.h
@@ -291,7 +291,7 @@ typedef struct mi_page_s {
   uint16_t              capacity;          // number of blocks committed, must be the first field, see `segment.c:page_clear`
   uint16_t              reserved;          // number of blocks reserved in memory
   mi_page_flags_t       flags;             // `in_full` and `has_aligned` flags (8 bits)
-  uint8_t               is_zero:1;         // `true` if the blocks in the free list are zero initialized
+  uint8_t               free_is_zero:1;    // `true` if the blocks in the free list are zero initialized
   uint8_t               retire_expire:7;   // expiration count for retired blocks
 
   mi_block_t*           free;              // list of available free blocks (`malloc` allocates from this list)
diff --git a/src/alloc-aligned.c b/src/alloc-aligned.c
index 65b28748..be62efda 100644
--- a/src/alloc-aligned.c
+++ b/src/alloc-aligned.c
@@ -222,7 +222,7 @@ static void* mi_heap_realloc_zero_aligned_at(mi_heap_t* heap, void* p, size_t ne
     if (newp != NULL) {
       if (zero && newsize > size) {
         const mi_page_t* page = _mi_ptr_page(newp);
-        if (page->is_zero) {
+        if (page->free_is_zero) {
           // already zero initialized
           mi_assert_expensive(mi_mem_is_zero(newp,newsize));
         }
diff --git a/src/alloc.c b/src/alloc.c
index 3edc0b51..ac167891 100644
--- a/src/alloc.c
+++ b/src/alloc.c
@@ -46,7 +46,7 @@ extern inline void* _mi_page_malloc(mi_heap_t* heap, mi_page_t* page, size_t siz
   // zero the block? note: we need to zero the full block size (issue #63)
   if mi_unlikely(zero) {
     mi_assert_internal(page->xblock_size != 0); // do not call with zero'ing for huge blocks (see _mi_malloc_generic)
-    if (page->is_zero) {
+    if (page->free_is_zero) {
       block->next = 0;
     }
     else {
diff --git a/src/page.c b/src/page.c
index 27c6fd09..c61677b6 100644
--- a/src/page.c
+++ b/src/page.c
@@ -84,7 +84,7 @@ static bool mi_page_is_valid_init(mi_page_t* page) {
   mi_assert_internal(mi_page_list_is_valid(page,page->local_free));
 
   #if MI_DEBUG>3 // generally too expensive to check this
-  if (page->is_zero) {
+  if (page->free_is_zero) {
     const size_t ubsize = mi_page_usable_block_size(page);
     for(mi_block_t* block = page->free; block != NULL; block = mi_block_next(page,block)) {
       mi_assert_expensive(mi_mem_is_zero(block + 1, ubsize - sizeof(mi_block_t)));
@@ -220,7 +220,7 @@ void _mi_page_free_collect(mi_page_t* page, bool force) {
       // usual case
       page->free = page->local_free;
       page->local_free = NULL;
-      page->is_zero = false;
+      page->free_is_zero = false;
     }
     else if (force) {
       // append -- only on shutdown (force) as this is a linear operation
@@ -232,7 +232,7 @@ void _mi_page_free_collect(mi_page_t* page, bool force) {
       mi_block_set_next(page, tail, page->free);
       page->free = page->local_free;
       page->local_free = NULL;
-      page->is_zero = false;
+      page->free_is_zero = false;
     }
   }
 
@@ -662,12 +662,9 @@ static void mi_page_init(mi_heap_t* heap, mi_page_t* page, size_t block_size, mi
   page->keys[0] = _mi_heap_random_next(heap);
   page->keys[1] = _mi_heap_random_next(heap);
   #endif
-  page->is_zero = page->is_zero_init;
-  #if MI_DEBUG>1
-  if (page->is_zero_init) {
-    mi_mem_is_zero(page_start, page_size);
-  }
-  #endif
+  page->free_is_zero = page->is_zero_init;
+  mi_assert_expensive(!page->is_zero_init || mi_mem_is_zero(page_start, page_size));
+  
   mi_assert_internal(page->capacity == 0);
   mi_assert_internal(page->free == NULL);
   mi_assert_internal(page->used == 0);