diff --git a/torba/tests/client_tests/unit/test_headers.py b/torba/tests/client_tests/unit/test_headers.py
index ca494b8e2..c0efa0624 100644
--- a/torba/tests/client_tests/unit/test_headers.py
+++ b/torba/tests/client_tests/unit/test_headers.py
@@ -109,7 +109,6 @@ class BasicHeadersTests(BitcoinHeadersTestCase):
         # corrupt by appending
         headers.io.seek(block_bytes(len(headers)))
         headers.io.write(b"appending")
-        headers._size = None
         await headers.repair()
         self.assertEqual(headers.height, 1499)
         await headers.connect(len(headers), self.get_bytes(block_bytes(3001 - 1500), after=block_bytes(1500)))
diff --git a/torba/torba/client/baseheader.py b/torba/torba/client/baseheader.py
index 22cc7aef6..3cd51800f 100644
--- a/torba/torba/client/baseheader.py
+++ b/torba/torba/client/baseheader.py
@@ -170,10 +170,12 @@ class BaseHeaders:
 
     async def repair(self):
         previous_header_hash = fail = None
-        self.io.seek(0)
-        batch_size = 10000
+        batch_size = 36
         for start_height in range(0, self.height, batch_size):
+            self.io.seek(self.header_size * start_height)
             headers = self.io.read(self.header_size*batch_size)
+            if len(headers) % self.header_size != 0:
+                headers = headers[:(len(headers) // self.header_size) * self.header_size]
             for header_hash, header in self._iterate_headers(start_height, headers):
                 height = header['block_height']
                 if height:
@@ -205,7 +207,7 @@ class BaseHeaders:
             end = min(len(headers), end + self.chunk_size * self.header_size)
 
     def _iterate_headers(self, height: int, headers: bytes) -> Iterator[Tuple[bytes, dict]]:
-        assert len(headers) % self.header_size == 0
+        assert len(headers) % self.header_size == 0, len(headers)
         for idx in range(len(headers) // self.header_size):
             start, end = idx * self.header_size, (idx + 1) * self.header_size
             header = headers[start:end]