diff --git a/include/mimalloc/internal.h b/include/mimalloc/internal.h
index 2954eabd..2a21f34b 100644
--- a/include/mimalloc/internal.h
+++ b/include/mimalloc/internal.h
@@ -329,6 +329,14 @@ static inline uintptr_t _mi_divide_up(uintptr_t size, size_t divider) {
   return (divider == 0 ? size : ((size + divider - 1) / divider));
 }
 
+
+// clamp an integer
+static inline size_t _mi_clamp(size_t sz, size_t min, size_t max) {
+  if (sz < min) return min;
+  else if (sz > max) return max;
+  else return sz;
+}
+
 // Is memory zero initialized?
 static inline bool mi_mem_is_zero(const void* p, size_t size) {
   for (size_t i = 0; i < size; i++) {
diff --git a/src/arena.c b/src/arena.c
index 25ce56ec..445cc309 100644
--- a/src/arena.c
+++ b/src/arena.c
@@ -358,8 +358,14 @@ static bool mi_arena_reserve(size_t req_size, bool allow_large, mi_arena_id_t re
     arena_reserve = arena_reserve/4;  // be conservative if virtual reserve is not supported (for WASM for example)
   }
   arena_reserve = _mi_align_up(arena_reserve, MI_ARENA_BLOCK_SIZE);
+  arena_reserve = _mi_align_up(arena_reserve, MI_SEGMENT_SIZE);
   if (arena_count >= 8 && arena_count <= 128) {
-    arena_reserve = ((size_t)1<<(arena_count/8)) * arena_reserve;  // scale up the arena sizes exponentially
+    // scale up the arena sizes exponentially every 8 entries (128 entries get to 589TiB)
+    const size_t multiplier = (size_t)1 << _mi_clamp(arena_count/8, 0, 16 );
+    size_t reserve = 0;
+    if (!mi_mul_overflow(multiplier, arena_reserve, &reserve)) {
+      arena_reserve = reserve;
+    }
   }
   if (arena_reserve < req_size) return false;  // should be able to at least handle the current allocation size