diff --git a/parsedmarc/cli.py b/parsedmarc/cli.py
index cb1dcd7d..9a032f5c 100644
--- a/parsedmarc/cli.py
+++ b/parsedmarc/cli.py
@@ -56,7 +56,7 @@
 handler.setFormatter(formatter)
 logger.addHandler(handler)
 
-SEEN_AGGREGATE_REPORT_IDS = ExpiringDict(max_len=None, max_age_seconds=3600)
+SEEN_AGGREGATE_REPORT_IDS = ExpiringDict(max_len=100000000, max_age_seconds=3600)
 
 
 def _str_to_list(s):