diff --git a/src/applications/config/option/PhabricatorApplicationConfigOptions.php b/src/applications/config/option/PhabricatorApplicationConfigOptions.php
index d99cdf3101..491852eab6 100644
--- a/src/applications/config/option/PhabricatorApplicationConfigOptions.php
+++ b/src/applications/config/option/PhabricatorApplicationConfigOptions.php
@@ -21,7 +21,14 @@ abstract class PhabricatorApplicationConfigOptions extends Phobject {
     }
 
     if ($option->isCustomType()) {
-      return $option->getCustomObject()->validateOption($option, $value);
+      try {
+        return $option->getCustomObject()->validateOption($option, $value);
+      } catch (Exception $ex) {
+        // If custom validators threw exceptions, convert them to configuation
+        // validation exceptions so we repair the configuration and raise
+        // an error.
+        throw new PhabricatorConfigValidationException($ex->getMessage());
+      }
     }
 
     switch ($option->getType()) {
diff --git a/src/applications/maniphest/constants/ManiphestTaskPriority.php b/src/applications/maniphest/constants/ManiphestTaskPriority.php
index 6bd1460628..16a35a9e83 100644
--- a/src/applications/maniphest/constants/ManiphestTaskPriority.php
+++ b/src/applications/maniphest/constants/ManiphestTaskPriority.php
@@ -116,7 +116,15 @@ final class ManiphestTaskPriority extends ManiphestConstants {
     return $config;
   }
 
-  public static function validateConfiguration(array $config) {
+  public static function validateConfiguration($config) {
+    if (!is_array($config)) {
+      throw new Exception(
+        pht(
+          'Configuration is not valid. Maniphest priority configurations '.
+          'must be dictionaries.',
+          $config));
+    }
+
     foreach ($config as $key => $value) {
       if (!ctype_digit((string)$key)) {
         throw new Exception(