diff --git a/IkiWiki/Render.pm b/IkiWiki/Render.pm
index 632ec980b..d34e39e8a 100644
--- a/IkiWiki/Render.pm
+++ b/IkiWiki/Render.pm
@@ -155,7 +155,7 @@ sub genpage ($$) {
 
 sub scan ($) {
 	my $file=shift;
-	return if $scanned{$file};
+	return if ($config{rebuild} && $phase > PHASE_SCAN) || $scanned{$file};
 	$scanned{$file}=1;
 
 	debug(sprintf(gettext("scanning %s"), $file));
@@ -886,6 +886,10 @@ sub refresh () {
 
 	# At this point it becomes OK to start matching pagespecs.
 	$phase = PHASE_RENDER;
+	# Save some memory in full rebuilds: we no longer need to keep
+	# track of which pages we've scanned, because we can assume the
+	# answer is "all of them".
+	%scanned = () if $config{rebuild};
 
 	remove_del(@$del, @$internal_del);