diff --git a/src/applications/harbormaster/controller/HarbormasterBuildLogRenderController.php b/src/applications/harbormaster/controller/HarbormasterBuildLogRenderController.php
index 50b17523ca..4b36ba83d9 100644
--- a/src/applications/harbormaster/controller/HarbormasterBuildLogRenderController.php
+++ b/src/applications/harbormaster/controller/HarbormasterBuildLogRenderController.php
@@ -105,7 +105,13 @@ final class HarbormasterBuildLogRenderController
     $reads = $this->mergeOverlappingReads($reads);
 
     foreach ($reads as $key => $read) {
-      $data = $log->loadData($read['fetchOffset'], $read['fetchLength']);
+      $fetch_offset = $read['fetchOffset'];
+      $fetch_length = $read['fetchLength'];
+      if ($fetch_offset + $fetch_length > $log_size) {
+        $fetch_length = $log_size - $fetch_offset;
+      }
+
+      $data = $log->loadData($fetch_offset, $fetch_length);
 
       $offset = $read['fetchOffset'];
       $line = $read['fetchLine'];
diff --git a/src/applications/harbormaster/controller/HarbormasterBuildLogViewController.php b/src/applications/harbormaster/controller/HarbormasterBuildLogViewController.php
index 41f2aef8e5..40641795c5 100644
--- a/src/applications/harbormaster/controller/HarbormasterBuildLogViewController.php
+++ b/src/applications/harbormaster/controller/HarbormasterBuildLogViewController.php
@@ -16,6 +16,9 @@ final class HarbormasterBuildLogViewController
       return new Aphront404Response();
     }
 
+    $target = $log->getBuildTarget();
+    $build = $target->getBuild();
+
     $page_title = pht('Build Log %d', $log->getID());
 
     $log_view = id(new HarbormasterBuildLogView())
@@ -25,6 +28,9 @@ final class HarbormasterBuildLogViewController
 
     $crumbs = $this->buildApplicationCrumbs()
       ->addTextCrumb(pht('Build Logs'))
+      ->addTextCrumb(
+        pht('Build %d', $build->getID()),
+        $build->getURI())
       ->addTextCrumb($page_title)
       ->setBorder(true);
 
diff --git a/src/applications/harbormaster/controller/HarbormasterBuildViewController.php b/src/applications/harbormaster/controller/HarbormasterBuildViewController.php
index 4507139d47..0e09b4d658 100644
--- a/src/applications/harbormaster/controller/HarbormasterBuildViewController.php
+++ b/src/applications/harbormaster/controller/HarbormasterBuildViewController.php
@@ -363,12 +363,19 @@ final class HarbormasterBuildViewController
       $log_view->setLines($lines);
       $log_view->setStart($start);
 
+      $prototype_view = id(new PHUIButtonView())
+        ->setTag('a')
+        ->setHref($log->getURI())
+        ->setIcon('fa-file-text-o')
+        ->setText(pht('New View (Prototype)'));
+
       $header = id(new PHUIHeaderView())
         ->setHeader(pht(
           'Build Log %d (%s - %s)',
           $log->getID(),
           $log->getLogSource(),
           $log->getLogType()))
+        ->addActionLink($prototype_view)
         ->setSubheader($this->createLogHeader($build, $log))
         ->setUser($viewer);
 
diff --git a/src/applications/harbormaster/view/HarbormasterBuildLogView.php b/src/applications/harbormaster/view/HarbormasterBuildLogView.php
index 81705f3f49..e240aab510 100644
--- a/src/applications/harbormaster/view/HarbormasterBuildLogView.php
+++ b/src/applications/harbormaster/view/HarbormasterBuildLogView.php
@@ -44,28 +44,43 @@ final class HarbormasterBuildLogView extends AphrontView {
 
     $header->addActionLink($download_button);
 
-    $content_id = celerity_generate_unique_node_id();
-    $content_div = javelin_tag(
-      'div',
-      array(
-        'id' => $content_id,
-        'class' => 'harbormaster-log-view-loading',
-      ),
-      pht('Loading...'));
-
-    require_celerity_resource('harbormaster-css');
-
-    Javelin::initBehavior(
-      'harbormaster-log',
-      array(
-        'contentNodeID' => $content_id,
-        'renderURI' => $log->getRenderURI($this->getHighlightedLineRange()),
-      ));
-
     $box_view = id(new PHUIObjectBoxView())
       ->setBackground(PHUIObjectBoxView::BLUE_PROPERTY)
-      ->setHeader($header)
-      ->appendChild($content_div);
+      ->setHeader($header);
+
+    $has_linemap = $log->getLineMap();
+    if ($has_linemap) {
+      $content_id = celerity_generate_unique_node_id();
+      $content_div = javelin_tag(
+        'div',
+        array(
+          'id' => $content_id,
+          'class' => 'harbormaster-log-view-loading',
+        ),
+        pht('Loading...'));
+
+      require_celerity_resource('harbormaster-css');
+
+      Javelin::initBehavior(
+        'harbormaster-log',
+        array(
+          'contentNodeID' => $content_id,
+          'renderURI' => $log->getRenderURI($this->getHighlightedLineRange()),
+        ));
+
+      $box_view->appendChild($content_div);
+    } else {
+      $box_view->setFormErrors(
+        array(
+          pht(
+            'This older log is missing required rendering data. To rebuild '.
+            'rendering data, run: %s',
+            phutil_tag(
+              'tt',
+              array(),
+              '$ bin/harbormaster rebuild-log --force --id '.$log->getID())),
+        ));
+    }
 
     return $box_view;
   }