diff --git a/substrateinterface/base.py b/substrateinterface/base.py
index 2ca7788..7e9316d 100644
--- a/substrateinterface/base.py
+++ b/substrateinterface/base.py
@@ -2355,7 +2355,8 @@ def decode_block(block_data, block_data_hash=None):
 
                                     engine = bytes(log_digest[1][0])
                                     # Retrieve validator set
-                                    validator_set = self.query("Session", "Validators", block_hash=block_hash)
+                                    parent_hash = block_data['header']['parentHash']
+                                    validator_set = self.query("Session", "Validators", block_hash=parent_hash)
 
                                     if engine == b'BABE':
                                         babe_predigest = self.runtime_config.create_scale_object(