diff --git a/src/applications/harbormaster/controller/HarbormasterBuildViewController.php b/src/applications/harbormaster/controller/HarbormasterBuildViewController.php
--- a/src/applications/harbormaster/controller/HarbormasterBuildViewController.php
+++ b/src/applications/harbormaster/controller/HarbormasterBuildViewController.php
@@ -126,17 +126,28 @@
 
       $target_box->addPropertyList($properties, pht('Overview'));
 
-      $description = $build_target->getBuildStep()->getDescription();
-      if ($description) {
-        $rendered = PhabricatorMarkupEngine::renderOneObject(
-          id(new PhabricatorMarkupOneOff())
-            ->setContent($description)
-            ->setPreserveLinebreaks(true),
-          'default',
-          $viewer);
-
-        $properties->addSectionHeader(pht('Description'));
-        $properties->addTextContent($rendered);
+      $step = $build_target->getBuildStep();
+
+      if ($step) {
+        $description = $step->getDescription();
+        if ($description) {
+          $rendered = PhabricatorMarkupEngine::renderOneObject(
+            id(new PhabricatorMarkupOneOff())
+              ->setContent($description)
+              ->setPreserveLinebreaks(true),
+            'default',
+            $viewer);
+
+          $properties->addSectionHeader(pht('Description'));
+          $properties->addTextContent($rendered);
+        }
+      } else {
+        $target_box->setFormErrors(
+          array(
+            pht(
+              'This build step has since been deleted on the build plan.  '.
+              'Some information may be omitted.'),
+          ));
       }
 
       $details = $build_target->getDetails();
diff --git a/src/applications/harbormaster/query/HarbormasterBuildTargetQuery.php b/src/applications/harbormaster/query/HarbormasterBuildTargetQuery.php
--- a/src/applications/harbormaster/query/HarbormasterBuildTargetQuery.php
+++ b/src/applications/harbormaster/query/HarbormasterBuildTargetQuery.php
@@ -103,7 +103,7 @@
 
       foreach ($page as $target) {
         $target->attachBuildStep(
-          $steps[$target->getBuildStepPHID()]);
+          idx($steps, $target->getBuildStepPHID()));
       }
     }
 
diff --git a/src/applications/harbormaster/storage/build/HarbormasterBuildTarget.php b/src/applications/harbormaster/storage/build/HarbormasterBuildTarget.php
--- a/src/applications/harbormaster/storage/build/HarbormasterBuildTarget.php
+++ b/src/applications/harbormaster/storage/build/HarbormasterBuildTarget.php
@@ -117,7 +117,7 @@
     return $this->assertAttached($this->build);
   }
 
-  public function attachBuildStep(HarbormasterBuildStep $step) {
+  public function attachBuildStep(HarbormasterBuildStep $step = null) {
     $this->buildStep = $step;
     return $this;
   }