diff --git a/src/os.c b/src/os.c
index a5f12c17..f7b36258 100644
--- a/src/os.c
+++ b/src/os.c
@@ -206,20 +206,26 @@ static void* mi_win_virtual_allocx(void* addr, size_t size, size_t try_alignment
 }
 
 static void* mi_win_virtual_alloc(void* addr, size_t size, size_t try_alignment, DWORD flags) {
-  static size_t large_page_try_ok = 0;
+  static volatile uintptr_t large_page_try_ok = 0;
   void* p = NULL;
   if (use_large_os_page(size, try_alignment)) {
+<<<<<<< HEAD
     if (large_page_try_ok > 0) {
       // if a large page allocation fails, it seems the calls to VirtualAlloc get very expensive.
+=======
+    uintptr_t try_ok = mi_atomic_read(&large_page_try_ok);
+    if (try_ok > 0) {
+      // if a large page page allocation fails, it seems the calls to VirtualAlloc get very expensive.
+>>>>>>> use atomic ops to guard large page tries on windows
       // therefore, once a large page allocation failed, we don't try again for `large_page_try_ok` times.
-      large_page_try_ok--;
+      mi_atomic_compare_exchange(&large_page_try_ok, try_ok - 1, try_ok);
     }
     else {
       // large OS pages must always reserve and commit.
       p = mi_win_virtual_allocx(addr, size, try_alignment, MEM_LARGE_PAGES | MEM_COMMIT | MEM_RESERVE | flags);
       // fall back to non-large page allocation on error (`p == NULL`).
       if (p == NULL) {
-        large_page_try_ok = 10;  // on error, don't try again for the next N allocations
+        mi_atomic_write(&large_page_try_ok,10);  // on error, don't try again for the next N allocations
       }
     }
   }