diff --git a/include/mimalloc-internal.h b/include/mimalloc-internal.h
index 6455d57e..d886bcec 100644
--- a/include/mimalloc-internal.h
+++ b/include/mimalloc-internal.h
@@ -315,39 +315,24 @@ static inline mi_page_queue_t* mi_page_queue(const mi_heap_t* heap, size_t size)
 }
 
 
+
 //-----------------------------------------------------------
 // Page flags
 //-----------------------------------------------------------
-static inline uintptr_t mi_page_thread_id(const mi_page_t* page) {
-  return (page->flags & ~MI_PAGE_FLAGS_MASK);
-}
-
-static inline void mi_page_init_flags(mi_page_t* page, uintptr_t thread_id) {
-  mi_assert_internal((thread_id & MI_PAGE_FLAGS_MASK) == 0);
-  page->flags = thread_id;
-}
-
-static inline void mi_page_set_thread_id(mi_page_t* page, uintptr_t thread_id) {
-  mi_assert_internal((thread_id & MI_PAGE_FLAGS_MASK) == 0);
-  page->flags = thread_id | (page->flags & MI_PAGE_FLAGS_MASK);
-}
-
 static inline bool mi_page_is_in_full(const mi_page_t* page) {
-  return ((page->flags & 0x01) != 0);
+  return page->flags.in_full;
 }
 
 static inline void mi_page_set_in_full(mi_page_t* page, bool in_full) {
-  if (in_full) page->flags |= 0x01;
-          else page->flags &= ~0x01;
+  page->flags.in_full = in_full;
 }
 
 static inline bool mi_page_has_aligned(const mi_page_t* page) {
-  return ((page->flags & 0x02) != 0);
+  return page->flags.has_aligned;
 }
 
 static inline void mi_page_set_has_aligned(mi_page_t* page, bool has_aligned) {
-  if (has_aligned) page->flags |= 0x02;
-              else page->flags &= ~0x02;
+  page->flags.has_aligned = has_aligned;
 }
 
 
diff --git a/include/mimalloc-types.h b/include/mimalloc-types.h
index dd1f05e3..c20b663a 100644
--- a/include/mimalloc-types.h
+++ b/include/mimalloc-types.h
@@ -124,12 +124,15 @@ typedef enum mi_delayed_e {
 } mi_delayed_t;
 
 
-// Use the bottom 2 bits for the `in_full` and `has_aligned` flags
-// and the rest for the threadid (we assume tid's never use those lower 2 bits).
-// This allows a single test in `mi_free` to check for unlikely cases
-// (namely, non-local free, aligned free, or freeing in a full page)
-#define MI_PAGE_FLAGS_MASK  ((uintptr_t)0x03)
-typedef uintptr_t mi_page_flags_t;
+// The `in_full` and `has_aligned` page flags are put in a union to efficiently 
+// test if both are false (`value == 0`) in the `mi_free` routine.
+typedef union mi_page_flags_u {
+  uint16_t value;
+  struct {
+    bool in_full;
+    bool has_aligned;
+  };
+} mi_page_flags_t;
 
 // Thread free list.
 // We use the bottom 2 bits of the pointer for mi_delayed_t flags
@@ -163,12 +166,12 @@ typedef struct mi_page_s {
   // layout like this to optimize access in `mi_malloc` and `mi_free`
   uint16_t              capacity;          // number of blocks committed
   uint16_t              reserved;          // number of blocks reserved in memory
-                                           // 16 bits padding
+  mi_page_flags_t       flags;             // `in_full` and `has_aligned` flags (16 bits)
+
   mi_block_t*           free;              // list of available free blocks (`malloc` allocates from this list)
   #if MI_SECURE
   uintptr_t             cookie;            // random cookie to encode the free lists
   #endif
-  mi_page_flags_t       flags;             // threadid:62 | has_aligned:1 | in_full:1
   size_t                used;              // number of blocks in use (including blocks in `local_free` and `thread_free`)
   
   mi_block_t*           local_free;        // list of deferred free blocks by this thread (migrates to `free`)
@@ -181,12 +184,11 @@ typedef struct mi_page_s {
   struct mi_page_s*     next;              // next page owned by this thread with the same `block_size`
   struct mi_page_s*     prev;              // previous page owned by this thread with the same `block_size`
 
-// improve page index calculation
-#if (MI_INTPTR_SIZE==8 && MI_SECURE==0)
-  void*                 padding[1];        // 12 words on 64-bit
-#elif MI_INTPTR_SIZE==4
-  // void*                 padding[1];         // 12 words on 32-bit
-#endif
+  // improve page index calculation
+  // without padding: 10 words on 64-bit, 11 on 32-bit. Secure adds one word
+  #if (MI_INTPTR_SIZE==8 && MI_SECURE>0) || (MI_INTPTR_SIZE==4 && MI_SECURE==0)
+  void*                 padding[1];        // 12 words on 64-bit in secure mode, 12 words on 32-bit plain
+  #endif
 } mi_page_t;
 
 
diff --git a/src/alloc.c b/src/alloc.c
index 9be2ef40..b7881ea5 100644
--- a/src/alloc.c
+++ b/src/alloc.c
@@ -225,19 +225,19 @@ void mi_free(void* p) mi_attr_noexcept
   }
 #endif
 
+  const uintptr_t tid = _mi_thread_id();
   mi_page_t* const page = _mi_segment_page_of(segment, p);
 
 #if (MI_STAT>1)
   mi_heap_t* heap = mi_heap_get_default();
-  mi_heap_stat_decrease( heap, malloc, mi_usable_size(p));
+  mi_heap_stat_decrease(heap, malloc, mi_usable_size(p));
   if (page->block_size <= MI_LARGE_OBJ_SIZE_MAX) {
-    mi_heap_stat_decrease( heap, normal[_mi_bin(page->block_size)], 1);
+    mi_heap_stat_decrease(heap, normal[_mi_bin(page->block_size)], 1);
   }
   // huge page stat is accounted for in `_mi_page_retire`
 #endif
 
-  const uintptr_t tid = _mi_thread_id();
-  if (mi_likely(tid == page->flags)) {  // if equal, the thread id matches and it is not a full page, nor has aligned blocks
+  if (mi_likely(tid == segment->thread_id && page->flags.value == 0)) {  // the thread id matches and it is not a full page, nor has aligned blocks
     // local, and not full or aligned
     mi_block_t* block = (mi_block_t*)p;
     mi_block_set_next(page, block, page->local_free);
@@ -247,7 +247,7 @@ void mi_free(void* p) mi_attr_noexcept
   }
   else {
     // non-local, aligned blocks, or a full page; use the more generic path
-    mi_free_generic(segment, page, tid == mi_page_thread_id(page), p);
+    mi_free_generic(segment, page, tid == segment->thread_id, p);
   }
 }
 
diff --git a/src/init.c b/src/init.c
index ec64def8..76e586f2 100644
--- a/src/init.c
+++ b/src/init.c
@@ -13,15 +13,16 @@ terms of the MIT license. A copy of the license can be found in the file
 // Empty page used to initialize the small free pages array
 const mi_page_t _mi_page_empty = {
   0, false, false, false, 0, 0,
+  { 0 },
   NULL,    // free
   #if MI_SECURE
   0,
   #endif
-  0, 0, // flags, used
+  0,       // used
   NULL, 0, 0,
   0, NULL, NULL, NULL
-  #if (MI_INTPTR_SIZE==8 && MI_SECURE==0)
-  , { NULL }
+  #if (MI_INTPTR_SIZE==8 && MI_SECURE>0) || (MI_INTPTR_SIZE==4 && MI_SECURE==0)
+  , { NULL } // padding
   #endif
 };
 
@@ -350,7 +351,7 @@ void mi_thread_init(void) mi_attr_noexcept
     pthread_setspecific(mi_pthread_key, (void*)(_mi_thread_id()|1)); // set to a dummy value so that `mi_pthread_done` is called
   #endif
 
-  #if (MI_DEBUG>0) // not in release mode as that leads to crashes on Windows dynamic override
+  #if (MI_DEBUG>0) && !defined(NDEBUG) // not in release mode as that leads to crashes on Windows dynamic override
   _mi_verbose_message("thread init: 0x%zx\n", _mi_thread_id());
   #endif
 }
diff --git a/src/page.c b/src/page.c
index 549ced38..a7b4a760 100644
--- a/src/page.c
+++ b/src/page.c
@@ -75,7 +75,6 @@ static bool mi_page_is_valid_init(mi_page_t* page) {
   mi_segment_t* segment = _mi_page_segment(page);
   uint8_t* start = _mi_page_start(segment,page,NULL);
   mi_assert_internal(start == _mi_segment_page_start(segment,page,page->block_size,NULL));
-  mi_assert_internal(segment->thread_id==0 || segment->thread_id == mi_page_thread_id(page));
   //mi_assert_internal(start + page->capacity*page->block_size == page->top);
 
   mi_assert_internal(mi_page_list_is_valid(page,page->free));
diff --git a/src/segment.c b/src/segment.c
index 6379b24a..b1a5221c 100644
--- a/src/segment.c
+++ b/src/segment.c
@@ -549,14 +549,11 @@ static void mi_segment_abandon(mi_segment_t* segment, mi_segments_tld_t* tld) {
   mi_assert_internal(segment->used > 0);
   mi_assert_internal(segment->abandoned_next == NULL);
   mi_assert_expensive(mi_segment_is_valid(segment));
-#if MI_DEBUG>1
-  for (size_t i = 0; i < segment->capacity; i++) {
-    mi_assert_internal(!segment->pages[i].segment_in_use || mi_page_thread_id(&segment->pages[i]) == 0);
-  }
-#endif
+
   // remove the segment from the free page queue if needed
   mi_segment_remove_from_free_queue(segment,tld);
   mi_assert_internal(segment->next == NULL && segment->prev == NULL);
+
   // all pages in the segment are abandoned; add it to the abandoned list
   _mi_stat_increase(&tld->stats->segments_abandoned, 1);
   mi_segments_track_size(-((long)segment->segment_size), tld);
@@ -570,11 +567,10 @@ static void mi_segment_abandon(mi_segment_t* segment, mi_segments_tld_t* tld) {
 }
 
 void _mi_segment_page_abandon(mi_page_t* page, mi_segments_tld_t* tld) {
-  mi_assert(page != NULL && mi_page_thread_id(page) != 0);
+  mi_assert(page != NULL);
   mi_segment_t* segment = _mi_page_segment(page);
   mi_assert_expensive(mi_segment_is_valid(segment));
-  segment->abandoned++;
-  mi_page_set_thread_id(page, 0);
+  segment->abandoned++;  
   _mi_stat_increase(&tld->stats->pages_abandoned, 1);
   mi_assert_internal(segment->abandoned <= segment->used);
   if (segment->used == segment->abandoned) {
@@ -626,7 +622,6 @@ bool _mi_segment_try_reclaim_abandoned( mi_heap_t* heap, bool try_all, mi_segmen
         }
         else {
           // otherwise reclaim it
-          mi_page_set_thread_id(page,segment->thread_id);
           _mi_page_reclaim(heap,page);
         }
       }
@@ -656,8 +651,7 @@ bool _mi_segment_try_reclaim_abandoned( mi_heap_t* heap, bool try_all, mi_segmen
 static mi_page_t* mi_segment_page_alloc_in(mi_segment_t* segment, mi_segments_tld_t* tld) {
   mi_assert_internal(mi_segment_has_free(segment));
   mi_page_t* page = mi_segment_find_free(segment, tld->stats);
-  page->segment_in_use = true;
-  mi_page_init_flags(page,segment->thread_id);
+  page->segment_in_use = true;  
   segment->used++;
   mi_assert_internal(segment->used <= segment->capacity);
   if (segment->used == segment->capacity) {
@@ -697,7 +691,6 @@ static mi_page_t* mi_segment_large_page_alloc(mi_segments_tld_t* tld, mi_os_tld_
   segment->used = 1;
   mi_page_t* page = &segment->pages[0];
   page->segment_in_use = true;
-  mi_page_init_flags(page,segment->thread_id);
   return page;
 }
 
@@ -709,7 +702,6 @@ static mi_page_t* mi_segment_huge_page_alloc(size_t size, mi_segments_tld_t* tld
   segment->used = 1;
   mi_page_t* page = &segment->pages[0];
   page->segment_in_use = true;
-  mi_page_init_flags(page,segment->thread_id);
   return page;
 }