diff -r 2f88a7c13a28 -r d7129285ac32 src/hash_map.c
--- a/src/hash_map.c	Tue Mar 21 17:18:29 2023 +0100
+++ b/src/hash_map.c	Tue Mar 21 17:21:20 2023 +0100
@@ -432,7 +432,12 @@
     map->base.cl = &cx_hash_map_class;
     map->base.allocator = allocator;
     map->base.size = 0;
-    map->base.itemsize = itemsize;
+
+    if (itemsize > 0) {
+        map->base.itemsize = itemsize;
+    } else {
+        cxMapStorePointers((CxMap *) map);
+    }
 
     return (CxMap *) map;
 }