--- a/lib/Mail/SpamAssassin/Conf.pm
+++ b/lib/Mail/SpamAssassin/Conf.pm
@@ -2086,6 +2086,22 @@
 =cut
 
   push (@cmds, {
+    setting => 'bayes_expiry_max_exponent',
+    default => 9,
+    type => $CONF_TYPE_NUMERIC,
+  });
+
+=item bayes_expiry_max_exponent		(default: 9)
+
+How far should be looked back in time to find an appropriate cut-off point.
+
+6 = 32 days
+9 = 256 days
+11 = 1024 days
+
+=cut
+
+  push (@cmds, {
     setting => 'bayes_expiry_max_db_size',
     default => 150000,
     type => $CONF_TYPE_NUMERIC,
