diff --git a/Lib/email/contentmanager.py b/Lib/email/contentmanager.py
index 2b4b875..b91fb0e 100644
--- a/Lib/email/contentmanager.py
+++ b/Lib/email/contentmanager.py
@@ -146,7 +146,7 @@
     def normal_body(lines): return b'\n'.join(lines) + b'\n'
     if cte==None:
         # Use heuristics to decide on the "best" encoding.
-        if max(len(x) for x in lines) <= policy.max_line_length:
+        if max((len(x) for x in lines), default=0) <= policy.max_line_length:
             try:
                 return '7bit', normal_body(lines).decode('ascii')
             except UnicodeDecodeError: