diff --git a/IkiWiki.pm b/IkiWiki.pm
index e7422cba5..db16a0854 100644
--- a/IkiWiki.pm
+++ b/IkiWiki.pm
@@ -899,7 +899,16 @@ sub loadindex () { #{{{
 		%pagesources=%pagemtime=%oldlinks=%links=%depends=
 		%destsources=%renderedfiles=%pagecase=%pagestate=();
 	}
-	open (my $in, "<", "$config{wikistatedir}/index") || return;
+	my $in;
+	if (! open ($in, "<", "$config{wikistatedir}/indexdb")) {
+		if (-e "$config{wikistatedir}/index") {
+			system("ikiwiki-transition", "indexdb", $config{wikistatedir});
+			open ($in, "<", "$config{wikistatedir}/indexdb") || return;
+		}
+		else {
+			return;
+		}
+	}
 	my $ret=Storable::fd_retrieve($in);
 	if (! defined $ret) {
 		return 0;
@@ -946,7 +955,7 @@ sub saveindex () { #{{{
 	if (! -d $config{wikistatedir}) {
 		mkdir($config{wikistatedir});
 	}
-	my $newfile="$config{wikistatedir}/index.new";
+	my $newfile="$config{wikistatedir}/indexdb.new";
 	my $cleanup = sub { unlink($newfile) };
 	open (my $out, '>', $newfile) || error("cannot write to $newfile: $!", $cleanup);
 	my %index;
@@ -976,8 +985,8 @@ sub saveindex () { #{{{
 	my $ret=Storable::nstore_fd(\%index, $out);
 	return if ! defined $ret || ! $ret;
 	close $out || error("failed saving to $newfile: $!", $cleanup);
-	rename($newfile, "$config{wikistatedir}/index") ||
-		error("failed renaming $newfile to $config{wikistatedir}/index", $cleanup);
+	rename($newfile, "$config{wikistatedir}/indexdb") ||
+		error("failed renaming $newfile to $config{wikistatedir}/indexdb", $cleanup);
 	
 	return 1;
 } #}}}
diff --git a/doc/ikiwiki-transition.mdwn b/doc/ikiwiki-transition.mdwn
index 118050a6c..da3b3a8d5 100644
--- a/doc/ikiwiki-transition.mdwn
+++ b/doc/ikiwiki-transition.mdwn
@@ -4,7 +4,7 @@ ikiwiki-transition - transition ikiwiki pages to new syntaxes
 
 # SYNOPSIS
 
-ikiwiki-transition prefix_directives page.mdwn...
+ikiwiki-transition type ...
 
 # DESCRIPTION
 
@@ -12,8 +12,8 @@ ikiwiki-transition prefix_directives page.mdwn...
 there's a major change in ikiwiki syntax.
 
 Currently only one such transition is handled, the `prefix_directives` mode
-converts an ikiwiki page from the old preprocessor directive syntax,
-requiring a space, to the new syntax, prefixed by '!'.
+converts the specified ikiwiki page from the old preprocessor directive
+syntax, requiring a space, to the new syntax, prefixed by '!'.
 
 Preprocessor directives which already use the new syntax will remain
 unchanged.
@@ -22,6 +22,12 @@ Note that if the page contains wiki links with spaces, which some
 older versions of ikiwiki accepted, the prefix_directives transition will
 treat these as preprocessor directives and convert them.
 
+One other transition is handled, the `indexdb` mode handles converting
+a plain text `.ikiwiki/index` file to a binary `.ikiwiki/indexdb`. In this
+mode, you should specify the srcdir of the wiki as the second parameter.
+You do not normally need to run `ikiwiki-transition indexdb`; ikiwiki will
+automatically run it as necessary.
+
 # AUTHOR
 
 Josh Triplett <josh@freedesktop.org>
diff --git a/ikiwiki-transition b/ikiwiki-transition
index 1fd23cec5..0e2bd4e22 100755
--- a/ikiwiki-transition
+++ b/ikiwiki-transition
@@ -1,6 +1,8 @@
 #!/usr/bin/perl -i
 use warnings;
 use strict;
+use IkiWiki;
+use HTML::Entities;
 
 my $regex = qr{
 	(\\?)		# 1: escape?
@@ -48,10 +50,32 @@ sub prefix_directives {
 	}
 }
 
+sub indexdb {
+	$config{wikistatedir}=shift()."/.ikiwiki";
+
+	if (! defined $config{wikistatedir}) {
+		usage();		
+	}
+
+	if (! IkiWiki::oldloadindex()) {
+		die "failed to load index\n";
+	}
+	if (! IkiWiki::saveindex()) {
+		die "failed to save indexdb\n"
+	}
+	if (! IkiWiki::loadindex()) {
+		die "transition failed, cannot load new indexdb\n";
+	}
+	if (! unlink("$config{wikistatedir}/index")) {
+		die "unlink failed: $!\n";
+	}
+}
+
 sub usage {
-	print STDERR "Usage: ikiwiki-transition type file ...\n";
-	print STDERR "Currently supported transition types:\n";
-	print STDERR "	prefix_directives\n";
+	print STDERR "Usage: ikiwiki-transition type ...\n";
+	print STDERR "Currently supported transition subcommands:\n";
+	print STDERR "	prefix_directives file\n";
+	print STDERR "	indexdb srcdir\n";
 	exit 1;
 }
 
@@ -61,6 +85,51 @@ my $mode=shift;
 if ($mode eq 'prefix_directives') {
 	prefix_directives(@ARGV);
 }
+elsif ($mode eq 'indexdb') {
+	indexdb(@ARGV);
+}
 else {
 	usage();
 }
+
+package IkiWiki;
+
+sub oldloadindex {
+	%oldrenderedfiles=%pagectime=();
+	if (! $config{rebuild}) {
+		%pagesources=%pagemtime=%oldlinks=%links=%depends=
+			%destsources=%renderedfiles=%pagecase=%pagestate=();
+	}
+	open (my $in, "<", "$config{wikistatedir}/index") || return;
+	while (<$in>) {
+		chomp;
+		my %items;
+		$items{link}=[];
+		$items{dest}=[];
+		foreach my $i (split(/ /, $_)) {
+			my ($item, $val)=split(/=/, $i, 2);
+			push @{$items{$item}}, decode_entities($val);
+		}
+
+		next unless exists $items{src}; # skip bad lines for now
+
+		my $page=pagename($items{src}[0]);
+		if (! $config{rebuild}) {
+			$pagesources{$page}=$items{src}[0];
+			$pagemtime{$page}=$items{mtime}[0];
+			$oldlinks{$page}=[@{$items{link}}];
+			$links{$page}=[@{$items{link}}];
+			$depends{$page}=$items{depends}[0] if exists $items{depends};
+			$destsources{$_}=$page foreach @{$items{dest}};
+			$renderedfiles{$page}=[@{$items{dest}}];
+			$pagecase{lc $page}=$page;
+			foreach my $k (grep /_/, keys %items) {
+				my ($id, $key)=split(/_/, $k, 2);
+				$pagestate{$page}{decode_entities($id)}{decode_entities($key)}=$items{$k}[0];
+			}
+		}
+		$oldrenderedfiles{$page}=[@{$items{dest}}];
+		$pagectime{$page}=$items{ctime}[0];
+	}
+	return close($in);
+}