diff --git a/IkiWiki/Plugin/mercurial.pm b/IkiWiki/Plugin/mercurial.pm
index e64e00512..102b4692b 100644
--- a/IkiWiki/Plugin/mercurial.pm
+++ b/IkiWiki/Plugin/mercurial.pm
@@ -307,7 +307,23 @@ sub rcs_recentchanges ($) {
 }
 
 sub rcs_diff ($;$) {
-	# TODO
+	my $rev=shift;
+	my $maxlines=shift;
+	my @lines;
+	my $addlines=sub {
+		my $line=shift;
+		return if defined $maxlines && @lines == $maxlines;
+		push @lines, $line."\n"
+			if (@lines || $line=~/^diff --git/);
+		return 1;
+	};
+	safe_hg(undef, $addlines, "hg", "diff", "-c", $rev, "-g");
+	if (wantarray) {
+		return @lines;
+	}
+	else {
+		return join("", @lines);
+	}
 }
 
 {
diff --git a/debian/changelog b/debian/changelog
index 5e9c91016..6499a40b1 100644
--- a/debian/changelog
+++ b/debian/changelog
@@ -1,12 +1,13 @@
 ikiwiki (3.20110716) UNRELEASED; urgency=low
 
-  * mercurial: openid nicknames are now used when committing. (Daniel Andersson)
-  * mercurial: implement rcs_commit_staged so comments, attachments, etc
+  * mercurial: Openid nicknames are now used when committing. (Daniel Andersson)
+  * mercurial: Implement rcs_commit_staged so comments, attachments, etc
     can be used. (Daniel Andersson)
-  * mercurial: implement rcs_rename and rcs_remove. (Daniel Andersson)
-  * mercurial: fix viewing of a diff containing non-utf8 changes.
+  * mercurial: Implement rcs_rename, rcs_remove. (Daniel Andersson)
+  * mercurial: Fix viewing of a diff containing non-utf8 changes.
     (Daniel Andersson)
   * mercurial: Make both rcs_getctime and rcs_getmtime fast. (Daniel Andersson)
+  * mercurial: Implement rcs_diff. (Daniel Andersson)
 
  -- Joey Hess <joeyh@debian.org>  Tue, 19 Jul 2011 11:22:52 -0400
 
diff --git a/doc/rcs.mdwn b/doc/rcs.mdwn
index 61aa76410..1f6b3c24e 100644
--- a/doc/rcs.mdwn
+++ b/doc/rcs.mdwn
@@ -20,7 +20,7 @@ auto.setup          |yes    |yes    |incomplete|yes         |incomplete   |yes
 `rcs_commit_staged` |yes    |yes    |yes       |yes         |yes          |yes      |no        |yes
 `rcs_rename`        |yes    |yes    |yes       |yes         |yes          |yes      |no        |yes
 `rcs_remove`        |yes    |yes    |yes       |yes         |yes          |yes      |no        |yes
-`rcs_diff`          |yes    |yes    |yes       |yes         |no           |yes      |yes       |yes
+`rcs_diff`          |yes    |yes    |yes       |yes         |yes          |yes      |yes       |yes
 `rcs_getctime`      |fast   |slow   |slow      |slow        |fast         |slow     |slow      |slow
 `rcs_getmtime`      |fast   |slow   |slow      |slow        |fast         |no       |no        |no
 `rcs_preprevert`    |yes    |no     |no        |no          |no           |no       |no        |no
diff --git a/doc/todo/rcs__95__diff_implementation_for_Mercurial_backend__44___based_on_Git_backend.mdwn b/doc/todo/rcs__95__diff_implementation_for_Mercurial_backend__44___based_on_Git_backend.mdwn
index 8843e0c86..42cfe1a19 100644
--- a/doc/todo/rcs__95__diff_implementation_for_Mercurial_backend__44___based_on_Git_backend.mdwn
+++ b/doc/todo/rcs__95__diff_implementation_for_Mercurial_backend__44___based_on_Git_backend.mdwn
@@ -6,6 +6,8 @@ CC of `rcs_diff` implementation in `git.pm` with few changes. Mercurial provides
 
 --[[Daniel Andersson]]
 
+> Guess that makes sense, [[done]] --[[Joey]] 
+
 ---
 
 	diff -r 1b6c46b62a28 -r cc73d670bf99 Plugin/mercurial.pm