diff --git a/electrum/blockchain.py b/electrum/blockchain.py
index 84c4c8af1..3614dfd1e 100644
--- a/electrum/blockchain.py
+++ b/electrum/blockchain.py
@@ -227,7 +227,7 @@ class Blockchain(util.PrintError):
     def verify_chunk(self, index: int, data: bytes) -> None:
         num = len(data) // HEADER_SIZE
         start_height = index * 2016
-        header = read_header(start_height)
+        header = self.read_header(start_height)
         prev_hash = self.get_hash(start_height - 1)
         bits, target = self.get_target2(start_height, header)
         for i in range(num):