diff --git a/include/mimalloc/prim.h b/include/mimalloc/prim.h
index 40f5d2d7..9e560696 100644
--- a/include/mimalloc/prim.h
+++ b/include/mimalloc/prim.h
@@ -47,7 +47,8 @@ int _mi_prim_alloc(size_t size, size_t try_alignment, bool commit, bool allow_la
 
 // Commit memory. Returns error code or 0 on success.
 // For example, on Linux this would make the memory PROT_READ|PROT_WRITE.
-int _mi_prim_commit(void* addr, size_t size);
+// `is_zero` is set to true if the memory was zero initialized (e.g. on Windows)
+int _mi_prim_commit(void* addr, size_t size, bool* is_zero);
 
 // Decommit memory. Returns error code or 0 on success. The `needs_recommit` result is true
 // if the memory would need to be re-committed. For example, on Windows this is always true,
diff --git a/src/os.c b/src/os.c
index f243f7a4..1b435335 100644
--- a/src/os.c
+++ b/src/os.c
@@ -405,12 +405,17 @@ bool _mi_os_commit(void* addr, size_t size, bool* is_zero, mi_stats_t* tld_stats
   if (csize == 0) return true;
 
   // commit  
-  int err = _mi_prim_commit(start, csize); 
+  bool os_is_zero = false;
+  int err = _mi_prim_commit(start, csize, &os_is_zero); 
   if (err != 0) {
     _mi_warning_message("cannot commit OS memory (error: %d (0x%x), address: %p, size: 0x%zx bytes)\n", err, err, start, csize);
+    return false;
   }
-  mi_assert_internal(err == 0);
-  return (err == 0);
+  if (os_is_zero && is_zero != NULL) { 
+    *is_zero = true;
+    mi_assert_expensive(mi_mem_is_zero(start, csize));
+  } 
+  return true;
 }
 
 static bool mi_os_decommit_ex(void* addr, size_t size, bool* needs_recommit, mi_stats_t* tld_stats) {
diff --git a/src/prim/unix/prim.c b/src/prim/unix/prim.c
index 4349f578..9a542d3e 100644
--- a/src/prim/unix/prim.c
+++ b/src/prim/unix/prim.c
@@ -346,8 +346,9 @@ static void unix_mprotect_hint(int err) {
   
     
 
-int _mi_prim_commit(void* start, size_t size) {
+int _mi_prim_commit(void* start, size_t size, bool* is_zero) {
   // commit: ensure we can access the area
+  *is_zero = false;
   int err = mprotect(start, size, (PROT_READ | PROT_WRITE));
   if (err != 0) { err = errno; }  
   unix_mprotect_hint(err);
diff --git a/src/prim/wasi/prim.c b/src/prim/wasi/prim.c
index bf78a258..50511f0b 100644
--- a/src/prim/wasi/prim.c
+++ b/src/prim/wasi/prim.c
@@ -128,8 +128,9 @@ int _mi_prim_alloc(size_t size, size_t try_alignment, bool commit, bool allow_la
 // Commit/Reset/Protect
 //---------------------------------------------
 
-int _mi_prim_commit(void* addr, size_t size) {
+int _mi_prim_commit(void* addr, size_t size, bool* is_zero) {
   MI_UNUSED(addr); MI_UNUSED(size); 
+  *is_zero = false;
   return 0;
 }
 
diff --git a/src/prim/windows/prim.c b/src/prim/windows/prim.c
index 61532737..bde48a7d 100644
--- a/src/prim/windows/prim.c
+++ b/src/prim/windows/prim.c
@@ -259,14 +259,26 @@ int _mi_prim_alloc(size_t size, size_t try_alignment, bool commit, bool allow_la
 #pragma warning(disable:6250)   // suppress warning calling VirtualFree without MEM_RELEASE (for decommit)
 #endif
 
-int _mi_prim_commit(void* addr, size_t size) {
+int _mi_prim_commit(void* addr, size_t size, bool* is_zero) {
+  *is_zero = false;
+  /*
+  // zero'ing only happens on an initial commit... but checking upfront seems expensive..
+  _MEMORY_BASIC_INFORMATION meminfo; _mi_memzero_var(meminfo);
+  if (VirtualQuery(addr, &meminfo, size) > 0) {
+    if ((meminfo.State & MEM_COMMIT) == 0) {
+      *is_zero = true;
+    }
+  }
+  */
+  // commit
   void* p = VirtualAlloc(addr, size, MEM_COMMIT, PAGE_READWRITE);
-  return (p != NULL ? 0 : (int)GetLastError());  
+  if (p == NULL) return (int)GetLastError();
+  return 0;
 }
 
 int _mi_prim_decommit(void* addr, size_t size, bool* needs_recommit) {  
   BOOL ok = VirtualFree(addr, size, MEM_DECOMMIT);
-  *needs_recommit = true;  // for safetly, assume always decommitted even in the case of an error.
+  *needs_recommit = true;  // for safety, assume always decommitted even in the case of an error.
   return (ok ? 0 : (int)GetLastError());
 }