diff --git a/warcprox/writer.py b/warcprox/writer.py
index 23dbafb..44d21d3 100644
--- a/warcprox/writer.py
+++ b/warcprox/writer.py
@@ -44,7 +44,7 @@ class WarcWriter:
 
         self.gzip = options.gzip or False
         self.warc_filename = options.warc_filename or \
-            '{prefix}-{timestamp17}-{randomtoken}-{serialno}.warc'
+            '{prefix}-{timestamp17}-{randomtoken}-{serialno}'
         digest_algorithm = options.digest_algorithm or 'sha1'
         base32 = options.base32
         self.record_builder = warcprox.warc.WarcRecordBuilder(