diff --git a/deps.nix b/deps.nix
index 90505bd4..7a8c943d 100644
--- a/deps.nix
+++ b/deps.nix
@@ -20,6 +20,8 @@ with pkgs;
   perlPackages.DBDSQLite
   perlPackages.EmailSender
   perlPackages.TextTable
+  perlPackages.TextDiff
+  perlPackages.FileSlurp
   perlPackages.NetTwitterLite
   perlPackages.PadWalker
   perlPackages.DataDump
diff --git a/src/lib/Hydra/Controller/API.pm b/src/lib/Hydra/Controller/API.pm
index 630dfbda..f1ee9c81 100644
--- a/src/lib/Hydra/Controller/API.pm
+++ b/src/lib/Hydra/Controller/API.pm
@@ -10,6 +10,8 @@ use Hydra::Controller::Project;
 use JSON::Any;
 use DateTime;
 use Digest::SHA qw(sha256_hex);
+use Text::Diff;
+use File::Slurp;
 
 # !!! Rewrite this to use View::JSON.
 
@@ -213,7 +215,7 @@ sub scmdiff : Chained('api') PathPart('scmdiff') Args(0) {
     if($type eq "hg") {
         my $clonePath = scmPath . "/" . sha256_hex($uri);
         die if ! -d $clonePath;
-	$diff .= `(cd $clonePath ; hg log -r $rev1:$rev2)`;
+	$diff .= `(cd $clonePath ; hg log -r $rev1 -r $rev2 -b $branch)`;
 	$diff .= `(cd $clonePath ; hg diff -r $rev1:$rev2)`;
     } elsif ($type eq "git") {
         my $clonePath = scmPath . "/" . sha256_hex($uri.$branch);
@@ -226,4 +228,37 @@ sub scmdiff : Chained('api') PathPart('scmdiff') Args(0) {
     $c->forward('Hydra::View::Plain');
 }
 
+sub readNormalizedLog {
+    my ($file) = @_;
+    my $res = read_file($file);
+
+    $res =~ s/\/nix\/store\/[a-z0-9]*-/\/nix\/store\/...-/g;
+    $res =~ s/nix-build-[a-z0-9]*-/nix-build-...-/g;
+    $res =~ s/[0-9]{2}:[0-9]{2}:[0-9]{2}/00:00:00/g;
+    return $res;
+}
+
+sub logdiff : Chained('api') PathPart('logdiff') Args(2) {
+    my ($self, $c, $buildid1, $buildid2) = @_;
+
+    my $diff = "";
+
+    my $build1 = getBuild($c, $buildid1);
+    notFound($c, "Build with ID $buildid1 doesn't exist.")
+        if !defined $build1;
+    my $build2 = getBuild($c, $buildid2);
+    notFound($c, "Build with ID $buildid2 doesn't exist.")
+        if !defined $build2;
+
+    if (-f $build1->resultInfo->logfile && -f $build2->resultInfo->logfile) {
+        my $logtext1 = readNormalizedLog($build1->resultInfo->logfile);
+        my $logtext2 = readNormalizedLog($build2->resultInfo->logfile);
+        $diff = diff \$logtext1, \$logtext2;
+    } else {
+        $c->response->status(404);
+    }
+    $c->stash->{'plain'} = { data => (scalar $diff) || " " };
+    $c->forward('Hydra::View::Plain');
+}
+
 1;
diff --git a/src/lib/Hydra/Controller/Root.pm b/src/lib/Hydra/Controller/Root.pm
index d5977b36..8661007a 100644
--- a/src/lib/Hydra/Controller/Root.pm
+++ b/src/lib/Hydra/Controller/Root.pm
@@ -151,6 +151,7 @@ sub robots_txt : Path('robots.txt') {
         , uri_for('Root', 'status', [])
         , uri_for('Root', 'all', [])
         , uri_for('API', 'scmdiff', [])
+        , uri_for('API', 'logdiff', [],"*", "*")
         , uri_for('Project', 'all', ["*"])
         , channelUris('Root', ["*"])
         , channelUris('Project', ["*", "*"])
diff --git a/src/root/build.tt b/src/root/build.tt
index 82920c0b..8b23e777 100644
--- a/src/root/build.tt
+++ b/src/root/build.tt
@@ -184,15 +184,19 @@
 				[% INCLUDE renderBuildSteps type="Failed" %]
 			[% END %]
 
-            [% IF build.resultInfo.buildstatus != 0 && prevSuccessfulBuild %]
             <h2>Changes</h2>
-            Changes compared to last successful build:<br/>
             <br/> 
             <table>
                 <thead>
                     <th>Last successful build <tt>[% INCLUDE renderDateTime timestamp = prevSuccessfulBuild.timestamp %]</tt></th>
-                    [% IF prevSuccessfulBuild && firstBrokenBuild && firstBrokenBuild.id != build.id %]<th>First broken build <tt>[% INCLUDE renderDateTime timestamp = firstBrokenBuild.timestamp %]</tt></th>[% END %]
-                    <th>This build <tt>[% INCLUDE renderDateTime timestamp = build.timestamp %]</tt></th>
+                    [% IF prevSuccessfulBuild && firstBrokenBuild && firstBrokenBuild.id != build.id %]
+                        <th>First broken build <tt>[% INCLUDE renderDateTime timestamp = firstBrokenBuild.timestamp %]</tt><br/>
+                            <tt>[ <a href="[% c.uri_for(c.controller('API').action_for('logdiff') prevSuccessfulBuild.id firstBrokenBuild.id ) %]">log diff</a> ]</tt>
+                        </th>
+                    [% END %]
+                    <th>This build <tt>[% INCLUDE renderDateTime timestamp = build.timestamp %]</tt> <br/>
+                        <tt>[ <a href="[% c.uri_for(c.controller('API').action_for('logdiff') prevSuccessfulBuild.id build.id) %]">log diff</a> ]</tt>
+                    </th>
                 </thead>
                 <tr>
                     <td valign="center">[% INCLUDE renderBuildStatusIcon build=prevSuccessfulBuild size=32 %] [% INCLUDE renderFullBuildLink build=prevSuccessfulBuild %]</td>
@@ -205,7 +209,6 @@
                     <td>[% INCLUDE renderInputDiff build1=prevSuccessfulBuild , build2=build %]</td>
                 </tr>
             </table>
-            [% END %]
 
 			[% IF build.resultInfo.errormsg && build.resultInfo.buildstatus != 5 %]