diff --git a/u7/hash_table.py b/u7/hash_table.py
index 9cf8ef5..2f775cc 100644
--- a/u7/hash_table.py
+++ b/u7/hash_table.py
@@ -6,6 +6,8 @@ from unittest import result
 class HashTable:
     def __init__(self, capacity=10):
         """Vytvor prázdnu tabuľku s kladnou celočíselnou kapacitou."""
+        if not isinstance(capacity, int) or capacity <= 0:
+            raise ValueError("kapacita ma byt + a cela")
         self.empty = object()
         self.deleted = object()
         self._capacity = capacity