diff --git a/source/cachetools/containers/hashmap.d b/source/cachetools/containers/hashmap.d
index 510730c..63b61ca 100644
--- a/source/cachetools/containers/hashmap.d
+++ b/source/cachetools/containers/hashmap.d
@@ -760,7 +760,7 @@ struct HashMap(K, V, Allocator = Mallocator, bool GCRangesAllowed = true) {
 
     private struct _kvRange {
         int             _pos;
-        ulong           _buckets_num;
+        size_t          _buckets_num;
         BucketStorage   _buckets;
         this(this) {
             if (_buckets_num) {
@@ -2094,4 +2094,4 @@ unittest {
     HashMap!(int, int) map;
     map.resize(7);
     assert(map.size == 8, "expected 8 got %s".format(map.size));
-}
\ No newline at end of file
+}