diff --git a/azure-pipelines.yml b/azure-pipelines.yml
index 01133630..89710dce 100644
--- a/azure-pipelines.yml
+++ b/azure-pipelines.yml
@@ -103,6 +103,16 @@ jobs:
         CXX: clang++
         BuildType: debug-asan-clang
         cmakeExtraArgs: -DCMAKE_BUILD_TYPE=Debug -DMI_DEBUG_FULL=ON -DMI_TRACK_ASAN=ON
+      Debug UBSAN Clang:
+        CC: clang
+        CXX: clang++
+        BuildType: debug-ubsan-clang
+        cmakeExtraArgs: -DCMAKE_BUILD_TYPE=Debug -DMI_DEBUG_FULL=ON -DMI_DEBUG_UBSAN=ON
+      Debug TSAN Clang++:
+        CC: clang
+        CXX: clang++
+        BuildType: debug-tsan-clang-cxx
+        cmakeExtraArgs: -DCMAKE_BUILD_TYPE=Debug -DMI_USE_CXX=ON -DMI_DEBUG_TSAN=ON
       
   steps:
   - task: CMake@1
diff --git a/src/alloc.c b/src/alloc.c
index 301166eb..75d8999c 100644
--- a/src/alloc.c
+++ b/src/alloc.c
@@ -50,7 +50,7 @@ extern inline void* _mi_page_malloc(mi_heap_t* heap, mi_page_t* page, size_t siz
     _mi_memzero_aligned(block, zsize - MI_PADDING_SIZE);
   }
 
-#if (MI_DEBUG>0) && !MI_TRACK_ENABLED
+#if (MI_DEBUG>0) && !MI_TRACK_ENABLED && !MI_TSAN
   if (!page->is_zero && !zero && !mi_page_is_huge(page)) {
     memset(block, MI_DEBUG_UNINIT, mi_page_usable_block_size(page));
   }
@@ -406,7 +406,7 @@ static mi_decl_noinline void _mi_free_block_mt(mi_page_t* page, mi_block_t* bloc
   }
 
 
-  #if (MI_DEBUG!=0) && !MI_TRACK_ENABLED                    // note: when tracking, cannot use mi_usable_size with multi-threading
+  #if (MI_DEBUG!=0) && !MI_TRACK_ENABLED  && !MI_TSAN       // note: when tracking, cannot use mi_usable_size with multi-threading
   memset(block, MI_DEBUG_FREED, mi_usable_size(block));
   #endif
 
@@ -458,7 +458,7 @@ static inline void _mi_free_block(mi_page_t* page, bool local, mi_block_t* block
     // owning thread can free a block directly
     if mi_unlikely(mi_check_is_double_free(page, block)) return;
     mi_check_padding(page, block);
-    #if (MI_DEBUG!=0) && !MI_TRACK_ENABLED
+    #if (MI_DEBUG!=0) && !MI_TRACK_ENABLED  && !MI_TSAN
     memset(block, MI_DEBUG_FREED, mi_page_block_size(page));
     #endif
     mi_block_set_next(page, block, page->local_free);
@@ -546,7 +546,7 @@ void mi_free(void* p) mi_attr_noexcept
       if mi_unlikely(mi_check_is_double_free(page, block)) return;
       mi_check_padding(page, block);
       mi_stat_free(page, block);
-      #if (MI_DEBUG!=0) && !MI_TRACK_ENABLED
+      #if (MI_DEBUG!=0) && !MI_TRACK_ENABLED  && !MI_TSAN
       memset(block, MI_DEBUG_FREED, mi_page_block_size(page));
       #endif
       mi_track_free_size(p, mi_page_usable_size_of(page,block)); // faster then mi_usable_size as we already know the page and that p is unaligned
diff --git a/src/os.c b/src/os.c
index 242a4eef..f6cc1e68 100644
--- a/src/os.c
+++ b/src/os.c
@@ -411,7 +411,7 @@ 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) && !MI_TRACK_ENABLED
+  #if (MI_DEBUG>1) && !MI_TRACK_ENABLED // && !MI_TSAN
   if (MI_SECURE==0) {
     memset(start, 0, csize); // pretend it is eagerly reset
   }
diff --git a/src/page.c b/src/page.c
index 531293f3..aa9f1bde 100644
--- a/src/page.c
+++ b/src/page.c
@@ -92,10 +92,12 @@ static bool mi_page_is_valid_init(mi_page_t* page) {
   }
   #endif
 
+  #if !MI_TRACK_ENABLED && !MI_TSAN
   mi_block_t* tfree = mi_page_thread_free(page);
   mi_assert_internal(mi_page_list_is_valid(page, tfree));
   //size_t tfree_count = mi_page_list_count(page, tfree);
   //mi_assert_internal(tfree_count <= page->thread_freed + 1);
+  #endif
 
   size_t free_count = mi_page_list_count(page, page->free) + mi_page_list_count(page, page->local_free);
   mi_assert_internal(page->used + free_count == page->capacity);
diff --git a/src/region.c b/src/region.c
index 77b07eb5..6c8ffb79 100644
--- a/src/region.c
+++ b/src/region.c
@@ -315,7 +315,7 @@ static void* mi_region_try_alloc(size_t blocks, bool* commit, bool* large, bool*
   }
   mi_assert_internal(!_mi_bitmap_is_any_claimed(&region->reset, 1, blocks, bit_idx));
 
-  #if (MI_DEBUG>=2) && !MI_TRACK_ENABLED
+  #if (MI_DEBUG>=2) && !MI_TRACK_ENABLED  // && !MI_TSAN
   if (*commit) { ((uint8_t*)p)[0] = 0; }
   #endif
 
@@ -361,7 +361,7 @@ void* _mi_mem_alloc_aligned(size_t size, size_t alignment, size_t align_offset,
 
   if (p != NULL) {
     mi_assert_internal(((uintptr_t)p + align_offset) % alignment == 0);
-    #if (MI_DEBUG>=2) && !MI_TRACK_ENABLED
+    #if (MI_DEBUG>=2) && !MI_TRACK_ENABLED  // && !MI_TSAN
     if (*commit) { ((uint8_t*)p)[0] = 0; } // ensure the memory is committed
     #endif
   }
diff --git a/src/segment.c b/src/segment.c
index 6cdf4fe7..8a9c8fe1 100644
--- a/src/segment.c
+++ b/src/segment.c
@@ -1182,7 +1182,7 @@ 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 && !MI_TRACK_ENABLED
+#if MI_DEBUG>=2 && !MI_TRACK_ENABLED // && !MI_TSAN
   // verify it is committed
   _mi_segment_page_start(_mi_page_segment(page), page, sizeof(void*), NULL, NULL)[0] = 0;
 #endif
@@ -1206,7 +1206,7 @@ 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 && !MI_TRACK_ENABLED
+#if MI_DEBUG>=2 && !MI_TRACK_ENABLED // && !MI_TSAN
   _mi_segment_page_start(segment, page, sizeof(void*), NULL, NULL)[0] = 0;
 #endif
   return page;