diff --git a/include/mimalloc/internal.h b/include/mimalloc/internal.h
index 84460777..7af1e6e1 100644
--- a/include/mimalloc/internal.h
+++ b/include/mimalloc/internal.h
@@ -867,8 +867,10 @@ static inline mi_memid_t _mi_memid_none(void) {
   return _mi_memid_create(MI_MEM_NONE);
 }
 
-static inline mi_memid_t _mi_memid_create_os(bool committed, bool is_zero, bool is_large) {
+static inline mi_memid_t _mi_memid_create_os(void* base, size_t size, bool committed, bool is_zero, bool is_large) {
   mi_memid_t memid = _mi_memid_create(MI_MEM_OS);
+  memid.mem.os.base = base;
+  memid.mem.os.size = size;
   memid.initially_committed = committed;
   memid.initially_zero = is_zero;
   memid.is_pinned = is_large;
diff --git a/src/os.c b/src/os.c
index b370e52a..ba0a6419 100644
--- a/src/os.c
+++ b/src/os.c
@@ -324,7 +324,7 @@ void* _mi_os_alloc(size_t size, mi_memid_t* memid) {
   bool os_is_zero  = false;
   void* p = mi_os_prim_alloc(size, 0, true, false, &os_is_large, &os_is_zero);
   if (p != NULL) {
-    *memid = _mi_memid_create_os(true, os_is_zero, os_is_large);
+    *memid = _mi_memid_create_os(p, size, true, os_is_zero, os_is_large);
   }
   return p;
 }
@@ -342,10 +342,9 @@ void* _mi_os_alloc_aligned(size_t size, size_t alignment, bool commit, bool allo
   void* os_base = NULL;
   void* p = mi_os_prim_alloc_aligned(size, alignment, commit, allow_large, &os_is_large, &os_is_zero, &os_base );
   if (p != NULL) {
-    *memid = _mi_memid_create_os(commit, os_is_zero, os_is_large);
+    *memid = _mi_memid_create_os(p, size, commit, os_is_zero, os_is_large);
     memid->mem.os.base = os_base;
-    // memid->mem.os.alignment = alignment;
-    memid->mem.os.size += ((uint8_t*)p - (uint8_t*)os_base);  // todo: return from prim_alloc_aligned
+    memid->mem.os.size += ((uint8_t*)p - (uint8_t*)os_base);  // todo: return from prim_alloc_aligned?
   }
   return p;
 }
@@ -602,7 +601,7 @@ void* _mi_os_alloc_huge_os_pages(size_t pages, int numa_node, mi_msecs_t max_mse
   if (psize != NULL) *psize = 0;
   if (pages_reserved != NULL) *pages_reserved = 0;
   size_t size = 0;
-  uint8_t* start = mi_os_claim_huge_pages(pages, &size);
+  uint8_t* const start = mi_os_claim_huge_pages(pages, &size);
   if (start == NULL) return NULL; // or 32-bit systems
 
   // Allocate one page at the time but try to place them contiguously
@@ -658,7 +657,7 @@ void* _mi_os_alloc_huge_os_pages(size_t pages, int numa_node, mi_msecs_t max_mse
   if (psize != NULL) { *psize = page * MI_HUGE_OS_PAGE_SIZE; }
   if (page != 0) {
     mi_assert(start != NULL);
-    *memid = _mi_memid_create_os(true /* is committed */, all_zero, true /* is_large */);
+    *memid = _mi_memid_create_os(start, size, true /* is committed */, all_zero, true /* is_large */);
     memid->memkind = MI_MEM_OS_HUGE;
     mi_assert(memid->is_pinned);
     #ifdef MI_TRACK_ASAN