diff --git a/src/__phutil_library_map__.php b/src/__phutil_library_map__.php
--- a/src/__phutil_library_map__.php
+++ b/src/__phutil_library_map__.php
@@ -654,6 +654,7 @@
     'HarbormasterBuildCommand' => 'applications/harbormaster/storage/HarbormasterBuildCommand.php',
     'HarbormasterBuildDependencyDatasource' => 'applications/harbormaster/typeahead/HarbormasterBuildDependencyDatasource.php',
     'HarbormasterBuildEngine' => 'applications/harbormaster/engine/HarbormasterBuildEngine.php',
+    'HarbormasterBuildFailureException' => 'applications/harbormaster/exception/HarbormasterBuildFailureException.php',
     'HarbormasterBuildGraph' => 'applications/harbormaster/engine/HarbormasterBuildGraph.php',
     'HarbormasterBuildItem' => 'applications/harbormaster/storage/build/HarbormasterBuildItem.php',
     'HarbormasterBuildItemPHIDType' => 'applications/harbormaster/phid/HarbormasterBuildItemPHIDType.php',
@@ -3394,6 +3395,7 @@
     'HarbormasterBuildCommand' => 'HarbormasterDAO',
     'HarbormasterBuildDependencyDatasource' => 'PhabricatorTypeaheadDatasource',
     'HarbormasterBuildEngine' => 'Phobject',
+    'HarbormasterBuildFailureException' => 'Exception',
     'HarbormasterBuildGraph' => 'AbstractDirectedGraph',
     'HarbormasterBuildItem' => 'HarbormasterDAO',
     'HarbormasterBuildItemPHIDType' => 'PhabricatorPHIDType',
diff --git a/src/applications/harbormaster/exception/HarbormasterBuildFailureException.php b/src/applications/harbormaster/exception/HarbormasterBuildFailureException.php
new file mode 100644
--- /dev/null
+++ b/src/applications/harbormaster/exception/HarbormasterBuildFailureException.php
@@ -0,0 +1,5 @@
+<?php
+
+final class HarbormasterBuildFailureException extends Exception {
+
+}
diff --git a/src/applications/harbormaster/step/HarbormasterCommandBuildStepImplementation.php b/src/applications/harbormaster/step/HarbormasterCommandBuildStepImplementation.php
--- a/src/applications/harbormaster/step/HarbormasterCommandBuildStepImplementation.php
+++ b/src/applications/harbormaster/step/HarbormasterCommandBuildStepImplementation.php
@@ -68,7 +68,7 @@
     $log_stderr->finalize($start_stderr);
 
     if ($err) {
-      throw new Exception(pht('Command failed with error %d.', $err));
+      throw new HarbormasterBuildFailureException();
     }
   }
 
diff --git a/src/applications/harbormaster/worker/HarbormasterTargetWorker.php b/src/applications/harbormaster/worker/HarbormasterTargetWorker.php
--- a/src/applications/harbormaster/worker/HarbormasterTargetWorker.php
+++ b/src/applications/harbormaster/worker/HarbormasterTargetWorker.php
@@ -56,6 +56,10 @@
       // If the target wants to yield, let that escape without further
       // processing. We'll resume after the task retries.
       throw $ex;
+    } catch (HarbormasterBuildFailureException $ex) {
+      // A build step wants to fail explicitly.
+      $target->setTargetStatus(HarbormasterBuildTarget::STATUS_FAILED);
+      $target->save();
     } catch (Exception $ex) {
       phlog($ex);