diff --git a/src/lint/linter/ArcanistPyFlakesLinter.php b/src/lint/linter/ArcanistPyFlakesLinter.php
--- a/src/lint/linter/ArcanistPyFlakesLinter.php
+++ b/src/lint/linter/ArcanistPyFlakesLinter.php
@@ -99,4 +99,8 @@
     return $messages;
   }
 
+  protected function canCustomizeLintSeverities() {
+    return false;
+  }
+
 }