diff --git a/src/applications/feed/PhabricatorFeedStoryPublisher.php b/src/applications/feed/PhabricatorFeedStoryPublisher.php
index 6d968042aa..0262f86af9 100644
--- a/src/applications/feed/PhabricatorFeedStoryPublisher.php
+++ b/src/applications/feed/PhabricatorFeedStoryPublisher.php
@@ -61,10 +61,25 @@ final class PhabricatorFeedStoryPublisher {
   }
 
   public function publish() {
-    if (!$this->storyType) {
+    $class = $this->storyType;
+    if (!$class) {
       throw new Exception("Call setStoryType() before publishing!");
     }
 
+    if (!class_exists($class)) {
+      throw new Exception(
+        "Story type must be a valid class name and must subclass ".
+        "PhabricatorFeedStory. ".
+        "'{$class}' is not a loadable class.");
+    }
+
+    if (!is_subclass_of($class, 'PhabricatorFeedStory')) {
+      throw new Exception(
+        "Story type must be a valid class name and must subclass ".
+        "PhabricatorFeedStory. ".
+        "'{$class}' is not a subclass of PhabricatorFeedStory.");
+    }
+
     $chrono_key = $this->generateChronologicalKey();
 
     $story = new PhabricatorFeedStoryData();