diff --git a/techrec/forge.py b/techrec/forge.py
index bbc531d..f3e9e3c 100644
--- a/techrec/forge.py
+++ b/techrec/forge.py
@@ -212,7 +212,7 @@ async def create_mp3(
         raise Exception("timeout")  # TODO: make a specific TimeoutError
     if p.returncode != 0:
         raise OSError("return code was %d" % p.returncode)
-    if not validator(start, end, tmp_file.name):
+    if validator is not None and not validator(start, end, tmp_file.name):
         os.unlink(tmp_file.name)
         return False
     os.rename(tmp_file.name, outfile)