diff --git a/blockchain.py b/blockchain.py
index 9de43dd..6dd4574 100644
--- a/blockchain.py
+++ b/blockchain.py
@@ -55,7 +55,7 @@ class Blockchain:
                 return False
 
             # Check that the Proof of Work is correct
-            if not self.valid_proof(last_block['proof'], block['proof'], last_block['previous_hash']):
+            if not self.valid_proof(last_block['proof'], block['proof'], self.hash(last_block)):
                 return False
 
             last_block = block