diff --git a/src/HydraFrontend/lib/HydraFrontend/Controller/Root.pm b/src/HydraFrontend/lib/HydraFrontend/Controller/Root.pm
index 3afdbe55..8fac493e 100644
--- a/src/HydraFrontend/lib/HydraFrontend/Controller/Root.pm
+++ b/src/HydraFrontend/lib/HydraFrontend/Controller/Root.pm
@@ -139,6 +139,8 @@ sub nixlog :Local {
 
     my $step = $build->buildsteps->find({stepnr => $stepnr});
     return error($c, "Build $id doesn't have a build step $stepnr.") if !defined $step;
+
+    return error($c, "Build step $stepnr of build $id does not have a log file.") if $step->logfile eq "";
     
     $c->stash->{template} = 'log.tt';
     $c->stash->{id} = $id;
diff --git a/src/HydraFrontend/root/build.tt b/src/HydraFrontend/root/build.tt
index 8ef44b8e..aa45c7af 100644
--- a/src/HydraFrontend/root/build.tt
+++ b/src/HydraFrontend/root/build.tt
@@ -147,7 +147,11 @@
       <tr>
         <td>[% step.stepnr %]</td>
         <td>
-          Build of <tt>[% step.outpath %]</tt>
+          [% IF step.type == 0 %]
+            Build of <tt>[% step.outpath %]</tt>
+          [% ELSE %]
+            Substitution of <tt>[% step.outpath %]</tt>
+          [% END %]
         </td>
         <td>
           [% IF step.busy == 0 %]
@@ -164,7 +168,9 @@
           [% ELSE %]
             <strong class="error-msg">Failed: [% step.errormsg %]</strong>
           [% END %]
-          (<a href="[% c.uri_for('/nixlog' build.id step.stepnr) %]">log</a>)
+          [% IF step.logfile %]
+            (<a href="[% c.uri_for('/nixlog' build.id step.stepnr) %]">log</a>)
+          [% END %]
         </td>
       </tr>
     [% END %]
diff --git a/src/build.pl b/src/build.pl
index 3436e4d3..637bd19a 100644
--- a/src/build.pl
+++ b/src/build.pl
@@ -47,7 +47,6 @@ sub doBuild {
                 print STDERR "$_";
                 next;
             }
-            print STDERR "GOT $_";
             
             if (/^@\s+build-started\s+(\S+)\s+(\S+)\s+(\S+)\s+(\S+)$/) {
                 $db->txn_do(sub {
@@ -64,9 +63,9 @@ sub doBuild {
                 });
             }
             
-            if (/^@\s+build-succeeded\s+(\S+)\s+(\S+)$/) {
+            elsif (/^@\s+build-succeeded\s+(\S+)\s+(\S+)$/) {
+                my $drvPath = $1;
                 $db->txn_do(sub {
-                    my $drvPath = $1;
                     (my $step) = $db->resultset('Buildsteps')->search(
                         {id => $build->id, type => 0, drvpath => $drvPath}, {});
                     die unless $step;
@@ -77,9 +76,9 @@ sub doBuild {
                 });
             }
 
-            if (/^@\s+build-failed\s+(\S+)\s+(\S+)\s+(\S+)\s+(.*)$/) {
+            elsif (/^@\s+build-failed\s+(\S+)\s+(\S+)\s+(\S+)\s+(.*)$/) {
+                my $drvPath = $1;
                 $db->txn_do(sub {
-                    my $drvPath = $1;
                     (my $step) = $db->resultset('Buildsteps')->search(
                         {id => $build->id, type => 0, drvpath => $drvPath}, {});
                     if ($step) {
@@ -106,6 +105,51 @@ sub doBuild {
                     }
                 });
             }
+
+            elsif (/^@\s+substituter-started\s+(\S+)\s+(\S+)$/) {
+                my $outPath = $1;
+                $db->txn_do(sub {
+                    $db->resultset('Buildsteps')->create(
+                        { id => $build->id
+                        , stepnr => $buildStepNr++
+                        , type => 1 # = substitution
+                        , outpath => $1
+                        , busy => 1
+                        , starttime => time
+                        });
+                });
+            }
+
+            elsif (/^@\s+substituter-succeeded\s+(\S+)$/) {
+                my $outPath = $1;
+                $db->txn_do(sub {
+                    (my $step) = $db->resultset('Buildsteps')->search(
+                        {id => $build->id, type => 1, outpath => $outPath}, {});
+                    die unless $step;
+                    $step->busy(0);
+                    $step->status(0);
+                    $step->stoptime(time);
+                    $step->update;
+                });
+            }
+
+            elsif (/^@\s+substituter-failed\s+(\S+)\s+(\S+)\s+(\S+)$/) {
+                my $outPath = $1;
+                $db->txn_do(sub {
+                    (my $step) = $db->resultset('Buildsteps')->search(
+                        {id => $build->id, type => 1, outpath => $outPath}, {});
+                    die unless $step;
+                    $step->busy(0);
+                    $step->status(1);
+                    $step->errormsg($3);
+                    $step->stoptime(time);
+                    $step->update;
+                });
+            }
+
+            else {
+                print STDERR "unknown Nix trace message: $_";
+            }
         }
         
         close OUT;