diff -r e77ccf1c4bb3 -r 4d58cbcc9efa ucx/hash_map.c
--- a/ucx/hash_map.c	Sun Dec 07 20:16:59 2025 +0100
+++ b/ucx/hash_map.c	Fri Dec 19 17:53:18 2025 +0100
@@ -78,7 +78,7 @@
     cxFree(map->collection.allocator, map);
 }
 
-static void *cx_hash_map_put(
+static CxMapEntry cx_hash_map_put(
         CxMap *map,
         CxHashKey key,
         void *value
@@ -117,7 +117,7 @@
                 allocator,
                 sizeof(struct cx_hash_map_element_s) + map->collection.elem_size
         );
-        if (e == NULL) return NULL;
+        if (e == NULL) return (CxMapEntry){NULL, NULL}; // LCOV_EXCL_LINE
 
         // write the value
         if (value == NULL) {
@@ -130,10 +130,10 @@
 
         // copy the key
         void *kd = cxMalloc(allocator, key.len);
-        if (kd == NULL) {
+        if (kd == NULL) { // LCOV_EXCL_START
             cxFree(allocator, e);
-            return NULL;
-        }
+            return (CxMapEntry){NULL, NULL};
+        } // LCOV_EXCL_STOP
         memcpy(kd, key.data, key.len);
         e->key.data = kd;
         e->key.len = key.len;
@@ -152,8 +152,8 @@
         map->collection.size++;
     }
 
-    // return pointer to the element
-    return elm->data;
+    // return the entry
+    return (CxMapEntry){&elm->key, elm->data};
 }
 
 static void cx_hash_map_unlink(
@@ -414,8 +414,7 @@
         buckets = 16;
     }
 
-    struct cx_hash_map_s *map = cxCalloc(allocator, 1,
-                                         sizeof(struct cx_hash_map_s));
+    struct cx_hash_map_s *map = cxZalloc(allocator, sizeof(struct cx_hash_map_s));
     if (map == NULL) return NULL;
 
     // initialize hash map members
@@ -433,9 +432,12 @@
 
     if (itemsize > 0) {
         map->base.collection.elem_size = itemsize;
+        map->base.collection.advanced_cmp = cx_ccmp_memcmp;
+        map->base.collection.cmp_data = &map->base.collection.elem_size;
     } else {
         map->base.collection.elem_size = sizeof(void *);
         map->base.collection.store_pointer = true;
+        map->base.collection.simple_cmp = cx_cmp_ptr;
     }
 
     return (CxMap *) map;
@@ -447,15 +449,16 @@
 
         size_t new_bucket_count = (map->collection.size * 5) >> 1;
         if (new_bucket_count < hash_map->bucket_count) {
+            // LCOV_EXCL_START
             errno = EOVERFLOW;
             return 1;
-        }
+        } // LCOV_EXCL_STOP
         struct cx_hash_map_element_s **new_buckets = cxCalloc(
                 map->collection.allocator,
                 new_bucket_count, sizeof(struct cx_hash_map_element_s *)
         );
 
-        if (new_buckets == NULL) return 1;
+        if (new_buckets == NULL) return 1; // LCOV_EXCL_LINE
 
         // iterate through the elements and assign them to their new slots
         for (size_t slot = 0; slot < hash_map->bucket_count; slot++) {