diff --git a/ci/sanity-check.py b/ci/sanity-check.py
index 9797e54..4a76be1 100644
--- a/ci/sanity-check.py
+++ b/ci/sanity-check.py
@@ -4,9 +4,11 @@
 # - file is ordered by block height in descending order
 # - header hashes match header (by hashing)
 # - header hashes are unique
+# - binary block files have a correct bitcoin block header
 
 import csv
 import hashlib
+import os
 
 EXPECTED_COLUMNS = 3
 
@@ -42,6 +44,17 @@ def dsha256(d):
 
         hash_count[header_hash] = hash_count.get(header_hash, 0) + 1
 
+        blockfile = f"blocks/{height}-{header_hash}.bin"
+        if os.path.exists(blockfile):
+            print(f"checking block file: {blockfile}")
+            with open(blockfile, "rb") as block:
+                header_bytes = block.read(80)
+                calculated_header_hash = bytes(reversed(dsha256(header_bytes))).hex()
+                assert header_hash == calculated_header_hash
+
+                header_hex = header_bytes.hex()
+                assert header == header_hex
+
 hash_appeared_multiple_times = False
 for e in hash_count.items():
     header_hash, count = e