diff --git a/include/mimalloc-internal.h b/include/mimalloc-internal.h
index 11c3db2e..7f16544b 100644
--- a/include/mimalloc-internal.h
+++ b/include/mimalloc-internal.h
@@ -931,7 +931,7 @@ static inline size_t mi_bsr(uintptr_t x) {
 // (AMD Zen3+ (~2020) or Intel Ice Lake+ (~2017). See also issue #201 and pr #253. 
 // ---------------------------------------------------------------------------------
 
-#if defined(_WIN32) && (defined(_M_IX86) || defined(_M_X64))
+#if !MI_TRACK_ENABLED && defined(_WIN32) && (defined(_M_IX86) || defined(_M_X64))
 #include <intrin.h>
 #include <string.h>
 extern bool _mi_cpu_has_fsrm;
diff --git a/include/mimalloc-track.h b/include/mimalloc-track.h
index be15c757..200f2529 100644
--- a/include/mimalloc-track.h
+++ b/include/mimalloc-track.h
@@ -17,6 +17,9 @@ terms of the MIT license. A copy of the license can be found in the file
 #define MI_VALGRIND 1
 
 #if MI_VALGRIND
+
+#define MI_TRACK_ENABLED 1
+
 #include <valgrind/valgrind.h>
 #include <valgrind/memcheck.h>
 
@@ -29,6 +32,8 @@ terms of the MIT license. A copy of the license can be found in the file
 
 #else
 
+#define MI_TRACK_ENABLED 0
+
 #define mi_track_malloc(p,size,zero)  
 #define mi_track_resize(p,oldsize,newsize)  
 #define mi_track_free(p)              
diff --git a/src/alloc-aligned.c b/src/alloc-aligned.c
index 4b4c43cb..e72d363f 100644
--- a/src/alloc-aligned.c
+++ b/src/alloc-aligned.c
@@ -41,6 +41,9 @@ static mi_decl_noinline void* mi_heap_malloc_zero_aligned_at_fallback(mi_heap_t*
   if (aligned_p != p) mi_page_set_has_aligned(_mi_ptr_page(p), true);
   mi_assert_internal(((uintptr_t)aligned_p + offset) % alignment == 0);
   mi_assert_internal(p == _mi_page_ptr_unalign(_mi_ptr_segment(aligned_p), _mi_ptr_page(aligned_p), aligned_p));
+
+  mi_track_free(p);
+  mi_track_malloc(aligned_p,size,zero);
   return aligned_p;
 }
 
@@ -82,6 +85,7 @@ static void* mi_heap_malloc_zero_aligned_at(mi_heap_t* const heap, const size_t
       void* p = _mi_page_malloc(heap, page, padsize, zero); // TODO: inline _mi_page_malloc
       mi_assert_internal(p != NULL);
       mi_assert_internal(((uintptr_t)p + offset) % alignment == 0);
+      mi_track_malloc(p,size,zero);
       return p;
     }
   }
diff --git a/src/alloc.c b/src/alloc.c
index fe744f37..33e565bf 100644
--- a/src/alloc.c
+++ b/src/alloc.c
@@ -39,6 +39,7 @@ extern inline void* _mi_page_malloc(mi_heap_t* heap, mi_page_t* page, size_t siz
   mi_assert_internal(page->free == NULL || _mi_ptr_page(page->free) == page);
 
   // allow use of the block internally 
+  // todo: can we optimize this call away for non-zero'd release mode?
   mi_track_mem_undefined(block,mi_page_block_size(page));
 
   // zero the block? note: we need to zero the full block size (issue #63)
@@ -77,6 +78,7 @@ extern inline void* _mi_page_malloc(mi_heap_t* heap, mi_page_t* page, size_t siz
   for (size_t i = 0; i < maxpad; i++) { fill[i] = MI_DEBUG_PADDING; }
 #endif
 
+  // mark as no-access again
   mi_track_mem_noaccess(block,mi_page_block_size(page));
   return block;
 }
@@ -341,7 +343,7 @@ static void mi_stat_huge_free(const mi_page_t* page) {
 // Free
 // ------------------------------------------------------
 
-// multi-threaded free
+// multi-threaded free (or free in huge block)
 static mi_decl_noinline void _mi_free_block_mt(mi_page_t* page, mi_block_t* block)
 {
   // The padding check may access the non-thread-owned page for the key values.
@@ -349,6 +351,7 @@ static mi_decl_noinline void _mi_free_block_mt(mi_page_t* page, mi_block_t* bloc
   mi_check_padding(page, block);
   mi_padding_shrink(page, block, sizeof(mi_block_t)); // for small size, ensure we can fit the delayed thread pointers without triggering overflow detection
   #if (MI_DEBUG!=0)
+  mi_track_mem_undefined(block, mi_page_block_size(page));  // note: check padding may set parts to noaccess
   memset(block, MI_DEBUG_FREED, mi_usable_size(block));
   #endif
 
@@ -408,6 +411,7 @@ static inline void _mi_free_block(mi_page_t* page, bool local, mi_block_t* block
     if mi_unlikely(mi_check_is_double_free(page, block)) return;
     mi_check_padding(page, block);
     #if (MI_DEBUG!=0)
+    mi_track_mem_undefined(block, mi_page_block_size(page));  // note: check padding may set parts to noaccess
     memset(block, MI_DEBUG_FREED, mi_page_block_size(page));
     #endif
     mi_block_set_next(page, block, page->local_free);
@@ -486,6 +490,10 @@ void mi_free(void* p) mi_attr_noexcept
   mi_threadid_t tid = _mi_thread_id();
   mi_page_t* const page = _mi_segment_page_of(segment, p);
   mi_block_t* const block = (mi_block_t*)p;
+
+  #if MI_TRACK_ENABLED
+  const size_t track_bsize = mi_page_block_size(page);
+  #endif
   
   if mi_likely(tid == mi_atomic_load_relaxed(&segment->thread_id) && page->flags.full_aligned == 0) {  // the thread id matches and it is not a full page, nor has aligned blocks
     // local, and not full or aligned
@@ -493,7 +501,7 @@ void mi_free(void* p) mi_attr_noexcept
     mi_check_padding(page, block);
     mi_stat_free(page, block);
     #if (MI_DEBUG!=0)
-    mi_track_mem_undefined(block,mi_page_block_size(page));
+    mi_track_mem_undefined(block,track_bsize);  // note: check padding may set parts to noaccess
     memset(block, MI_DEBUG_FREED, mi_page_block_size(page));
     #endif
     mi_block_set_next(page, block, page->local_free);
@@ -505,10 +513,10 @@ void mi_free(void* p) mi_attr_noexcept
   else {
     // non-local, aligned blocks, or a full page; use the more generic path
     // note: recalc page in generic to improve code generation
-    mi_track_mem_undefined(block,mi_page_block_size(page));
+    mi_track_mem_undefined(block,track_bsize);
     mi_free_generic(segment, tid == segment->thread_id, p);
   }
-  mi_track_mem_noaccess(block,mi_page_block_size(page));
+  mi_track_mem_noaccess(block,track_bsize);  // cannot use mi_page_block_size as the segment might be deallocated by now
 }
 
 bool _mi_free_delayed_block(mi_block_t* block) {
@@ -641,10 +649,12 @@ void* _mi_heap_realloc_zero(mi_heap_t* heap, void* p, size_t newsize, bool zero)
   // else if size == 0 then reallocate to a zero-sized block (and don't return NULL, just as mi_malloc(0)).
   // (this means that returning NULL always indicates an error, and `p` will not have been freed in that case.)
   const size_t size = _mi_usable_size(p,"mi_realloc"); // also works if p == NULL (with size 0)
+  #if !MI_TRACK_ENABLED
   if mi_unlikely(newsize <= size && newsize >= (size / 2) && newsize > 0) {  // note: newsize must be > 0 or otherwise we return NULL for realloc(NULL,0)
     // todo: adjust potential padding to reflect the new size?
     return p;  // reallocation still fits and not more than 50% waste
   }
+  #endif
   void* newp = mi_heap_malloc(heap,newsize);
   if mi_likely(newp != NULL) {
     if (zero && newsize > size) {
diff --git a/src/os.c b/src/os.c
index 855cc3a7..1640657e 100644
--- a/src/os.c
+++ b/src/os.c
@@ -986,7 +986,7 @@ static bool mi_os_resetx(void* addr, size_t size, bool reset, mi_stats_t* stats)
         else _mi_stat_decrease(&stats->reset, csize);
   if (!reset) return true; // nothing to do on unreset!
 
-  #if (MI_DEBUG>1)
+  #if (MI_DEBUG>1) && !MI_TRACK_ENABLED
   if (MI_SECURE==0) {
     memset(start, 0, csize); // pretend it is eagerly reset
   }
diff --git a/src/segment.c b/src/segment.c
index f9edf04a..f68b3b76 100644
--- a/src/segment.c
+++ b/src/segment.c
@@ -476,6 +476,7 @@ static void mi_segment_os_free(mi_segment_t* segment, size_t segment_size, mi_se
     fully_committed = false;
   }
   _mi_mem_free(segment, segment_size, segment->memid, fully_committed, any_reset, tld->os);
+  //mi_track_mem_noaccess(segment,segment_size);
 }
 
 // called by threads that are terminating to free cached segments
@@ -588,9 +589,11 @@ static mi_segment_t* mi_segment_init(mi_segment_t* segment, size_t required, mi_
     segment->mem_is_pinned = (mem_large || is_pinned);
     segment->mem_is_committed = commit;    
     mi_segments_track_size((long)segment_size, tld);
-  }
+  }  
   mi_assert_internal(segment != NULL && (uintptr_t)segment % MI_SEGMENT_SIZE == 0);
   mi_assert_internal(segment->mem_is_pinned ? segment->mem_is_committed : true);  
+  //mi_track_mem_defined(segment,info_size);
+  
   mi_atomic_store_ptr_release(mi_segment_t, &segment->abandoned_next, NULL);  // tsan
   if (!pages_still_good) {
     // zero the segment info (but not the `mem` fields)
@@ -1208,7 +1211,7 @@ static mi_page_t* mi_segment_page_alloc(mi_heap_t* heap, size_t block_size, mi_p
   mi_assert_internal(free_queue->first != NULL);
   mi_page_t* const page = mi_segment_page_alloc_in(free_queue->first, tld);
   mi_assert_internal(page != NULL);
-#if MI_DEBUG>=2
+#if MI_DEBUG>=2 && !MI_TRACK_ENABLED
   // verify it is committed
   _mi_segment_page_start(_mi_page_segment(page), page, sizeof(void*), NULL, NULL)[0] = 0;
 #endif
@@ -1232,7 +1235,7 @@ static mi_page_t* mi_segment_large_page_alloc(mi_heap_t* heap, size_t block_size
   if (segment == NULL) return NULL;
   mi_page_t* page = mi_segment_find_free(segment, tld);
   mi_assert_internal(page != NULL);
-#if MI_DEBUG>=2
+#if MI_DEBUG>=2 && !MI_TRACK_ENABLED
   _mi_segment_page_start(segment, page, sizeof(void*), NULL, NULL)[0] = 0;
 #endif
   return page;
diff --git a/test/test-api.c b/test/test-api.c
index c56fb88d..1d427c01 100644
--- a/test/test-api.c
+++ b/test/test-api.c
@@ -72,7 +72,9 @@ int main(void) {
     result = (mi_calloc((size_t)&mi_calloc,SIZE_MAX/1000) == NULL);
   };
   CHECK_BODY("calloc0") {
-    result = (mi_usable_size(mi_calloc(0,1000)) <= 16);
+    void* p = mi_calloc(0,1000);
+    result = (mi_usable_size(p) <= 16);
+    mi_free(p);
   };
   CHECK_BODY("malloc-large") {   // see PR #544.
     void* p = mi_malloc(67108872);
diff --git a/test/test-wrong.c b/test/test-wrong.c
index 7544b7fd..b0e59834 100644
--- a/test/test-wrong.c
+++ b/test/test-wrong.c
@@ -11,7 +11,10 @@
 int main(int argc, char** argv) {
   int* p = mi(malloc)(3*sizeof(int));
   int* q = mi(malloc)(sizeof(int));
-  
+
+  int* r = mi_malloc_aligned(8,16);
+  mi_free(r);
+
   // undefined access
   // printf("undefined: %d\n", *q);
   
@@ -23,7 +26,7 @@ int main(int argc, char** argv) {
   mi(free)(q);
 
   // double free
-  mi(free)(q);
+  // mi(free)(q);
 
   // use after free
   printf("use-after-free: %d\n", *q);