lib/PublicInbox/DummyInbox.pm | 4 ++--
 lib/PublicInbox/IMAPD.pm      | 6 +++---
 lib/PublicInbox/Inbox.pm      | 2 ++

diff --git a/lib/PublicInbox/DummyInbox.pm b/lib/PublicInbox/DummyInbox.pm
index 69b0b6837c7b9a1cbff333a9d4c8fa4235ccf363..02426f13c42f7aa027dd52eb70f2c58f6c09fb1d 100644
--- a/lib/PublicInbox/DummyInbox.pm
+++ b/lib/PublicInbox/DummyInbox.pm
@@ -7,13 +7,13 @@ # so we have a dummy
 package PublicInbox::DummyInbox;
 use strict;
 
-sub created_at { 0 } # Msgmap::created_at
+sub uidvalidity { 0 } # Msgmap::created_at
 sub mm { shift }
 sub uid_range { [] } # Over::uid_range
 sub subscribe_unlock { undef };
 
 no warnings 'once';
-*max = \&created_at;
+*max = \&uidvalidity;
 *query_xover = \&uid_range;
 *over = \&mm;
 *search = *unsubscribe_unlock =
diff --git a/lib/PublicInbox/IMAPD.pm b/lib/PublicInbox/IMAPD.pm
index 3c211ee1bf111568b70040c2b97559f9a88c7580..bb705136aecd5ab86f6e71b9b0ff46b76b5508ec 100644
--- a/lib/PublicInbox/IMAPD.pm
+++ b/lib/PublicInbox/IMAPD.pm
@@ -38,13 +38,13 @@ 		return;
 	}
 	$ibx->over or return;
 	$ibx->{over} = undef;
-	my $mm = $ibx->mm or return;
-	$ibx->{mm} = undef;
 
 	# RFC 3501 2.3.1.1 -  "A good UIDVALIDITY value to use in
 	# this case is a 32-bit representation of the creation
 	# date/time of the mailbox"
-	defined($ibx->{uidvalidity} = $mm->created_at) or return;
+	eval { $ibx->uidvalidity };
+	my $mm = delete($ibx->{mm}) or return;
+	defined($ibx->{uidvalidity}) or return;
 	PublicInbox::IMAP::ensure_slices_exist($imapd, $ibx, $mm->max // 0);
 
 	# preload to avoid fragmentation:
diff --git a/lib/PublicInbox/Inbox.pm b/lib/PublicInbox/Inbox.pm
index b0894a7d6414d038d820afa4533a2c2f69321ddd..cbb95b8d6204ef756c9b551d9388954e2300c9dc 100644
--- a/lib/PublicInbox/Inbox.pm
+++ b/lib/PublicInbox/Inbox.pm
@@ -428,4 +428,6 @@ 		warn "E: $@ ($self->{inboxdir})\n" if $@;
 	}
 }
 
+sub uidvalidity  { $_[0]->{uidvalidity} //= $_[0]->mm->created_at }
+
 1;