diff --git a/lesson-1/chapter-13/Contract.sol b/lesson-1/chapter-13/Contract.sol
index 8e834a2..7fed6be 100644
--- a/lesson-1/chapter-13/Contract.sol
+++ b/lesson-1/chapter-13/Contract.sol
@@ -15,7 +15,8 @@ contract ZombieFactory {
     Zombie[] public zombies;
 
     function _createZombie(string _name, uint _dna) private {
-        uint id = zombies.push(Zombie(_name, _dna)) - 1;
+        zombies.push(Zombie(_name, _dna));
+        uint id = zombies.length - 1;
         emit NewZombie(id, _name, _dna);
     }
 
@@ -29,4 +30,4 @@ contract ZombieFactory {
         _createZombie(_name, randDna);
     }
 
-}
\ No newline at end of file
+}