diff --git a/src/s3ql/block_cache.py b/src/s3ql/block_cache.py
index a4b55fd1..267b9a12 100644
--- a/src/s3ql/block_cache.py
+++ b/src/s3ql/block_cache.py
@@ -86,10 +86,10 @@ class CacheEntry:
     def flush(self):
         self.fh.flush()
 
-    def seek(self, off):
+    def seek(self, off, whence=0):
         if self.pos != off:
-            self.fh.seek(off)
-            self.pos = off
+            self.fh.seek(off, whence)
+            self.pos = self.fh.tell()
 
     def tell(self):
         return self.pos