diff --git a/src/os.c b/src/os.c
index 5c38989d..4696a4d7 100644
--- a/src/os.c
+++ b/src/os.c
@@ -345,6 +345,17 @@ static void* mi_unix_mmapx(void* addr, size_t size, size_t try_alignment, int pr
   return p;
 }
 
+static int mi_unix_mmap_fd(void) {
+#if defined(VM_MAKE_TAG)
+  // macOS: tracking anonymous page with a specific ID. (All up to 98 are taken officially but LLVM sanitizers had taken 99)
+  int os_tag = (int)mi_option_get(mi_option_os_tag);
+  if (os_tag < 100 || os_tag > 255) os_tag = 100;
+  return VM_MAKE_TAG(os_tag);
+#else
+  return -1;
+#endif
+}
+
 static void* mi_unix_mmap(void* addr, size_t size, size_t try_alignment, int protect_flags, bool large_only, bool allow_large, bool* is_large) {
   void* p = NULL;
   #if !defined(MAP_ANONYMOUS)
@@ -354,7 +365,7 @@ static void* mi_unix_mmap(void* addr, size_t size, size_t try_alignment, int pro
   #define MAP_NORESERVE  0
   #endif
   int flags = MAP_PRIVATE | MAP_ANONYMOUS | MAP_NORESERVE;
-  int fd = -1;
+  const int fd = mi_unix_mmap_fd();
   #if defined(MAP_ALIGNED)  // BSD
   if (try_alignment > 0) {
     size_t n = _mi_bsr(try_alignment);
@@ -365,13 +376,7 @@ static void* mi_unix_mmap(void* addr, size_t size, size_t try_alignment, int pro
   #endif
   #if defined(PROT_MAX)
   protect_flags |= PROT_MAX(PROT_READ | PROT_WRITE); // BSD
-  #endif
-  #if defined(VM_MAKE_TAG)
-  // macOS: tracking anonymous page with a specific ID. (All up to 98 are taken officially but LLVM sanitizers had taken 99)
-  int os_tag = (int)mi_option_get(mi_option_os_tag);
-  if (os_tag < 100 || os_tag > 255) os_tag = 100;
-  fd = VM_MAKE_TAG(os_tag);
-  #endif
+  #endif  
   if ((large_only || use_large_os_page(size, try_alignment)) && allow_large) {
     static _Atomic(uintptr_t) large_page_try_ok; // = 0;
     uintptr_t try_ok = mi_atomic_load_acquire(&large_page_try_ok);
@@ -713,7 +718,8 @@ static bool mi_os_commitx(void* addr, size_t size, bool commit, bool conservativ
   #elif defined(MAP_FIXED)
   if (!commit) {
     // use mmap with MAP_FIXED to discard the existing memory (and reduce commit charge)
-    void* p = mmap(start, csize, PROT_NONE, (MAP_FIXED | MAP_PRIVATE | MAP_ANONYMOUS | MAP_NORESERVE), -1, 0);
+    const int fd = mi_unix_mmap_fd();
+    void* p = mmap(start, csize, PROT_NONE, (MAP_FIXED | MAP_PRIVATE | MAP_ANONYMOUS | MAP_NORESERVE), fd, 0);
     if (p != start) { err = errno; }
   }
   else {