diff --git a/blockchain.py b/blockchain.py
index 9de43dd..937d352 100644
--- a/blockchain.py
+++ b/blockchain.py
@@ -51,11 +51,12 @@ class Blockchain:
             print(f'{block}')
             print("\n-----------\n")
             # Check that the hash of the block is correct
-            if block['previous_hash'] != self.hash(last_block):
+            last_block_hash = self.hash(last_block)
+            if block['previous_hash'] != last_block_hash:
                 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'], last_block_hash):
                 return False
 
             last_block = block