diff --git a/src/lint/message/ArcanistLintMessage.php b/src/lint/message/ArcanistLintMessage.php
index 8fe9850e..7ee90a4b 100644
--- a/src/lint/message/ArcanistLintMessage.php
+++ b/src/lint/message/ArcanistLintMessage.php
@@ -188,6 +188,7 @@ final class ArcanistLintMessage {
   }
 
   public function setDependentMessages(array $messages) {
+    assert_instances_of($messages, 'ArcanistLintMessage');
     $this->dependentMessages = $messages;
     return $this;
   }
diff --git a/src/lint/message/__init__.php b/src/lint/message/__init__.php
index f40b8bd6..bf640281 100644
--- a/src/lint/message/__init__.php
+++ b/src/lint/message/__init__.php
@@ -5,7 +5,10 @@
  */
 
 
+
 phutil_require_module('arcanist', 'lint/severity');
 
+phutil_require_module('phutil', 'utils');
+
 
 phutil_require_source('ArcanistLintMessage.php');
diff --git a/src/parser/bundle/ArcanistBundle.php b/src/parser/bundle/ArcanistBundle.php
index 76ccd786..609bc7fa 100644
--- a/src/parser/bundle/ArcanistBundle.php
+++ b/src/parser/bundle/ArcanistBundle.php
@@ -546,7 +546,7 @@ final class ArcanistBundle {
   }
 
   private function buildHunkChanges(array $hunks) {
-
+    assert_instances_of($hunks, 'ArcanistDiffHunk');
     $result = array();
     foreach ($hunks as $hunk) {
       $small_hunks = $this->breakHunkIntoSmallHunks($hunk);
diff --git a/src/parser/diff/ArcanistDiffParser.php b/src/parser/diff/ArcanistDiffParser.php
index 08cafae6..f1614d68 100644
--- a/src/parser/diff/ArcanistDiffParser.php
+++ b/src/parser/diff/ArcanistDiffParser.php
@@ -58,6 +58,7 @@ final class ArcanistDiffParser {
   }
 
   public function setChanges(array $changes) {
+    assert_instances_of($changes, 'ArcanistDiffChange');
     $this->changes = mpull($changes, null, 'getCurrentPath');
     return $this;
   }
diff --git a/src/workflow/liberate/ArcanistLiberateWorkflow.php b/src/workflow/liberate/ArcanistLiberateWorkflow.php
index 03bf4601..81ddbc77 100644
--- a/src/workflow/liberate/ArcanistLiberateWorkflow.php
+++ b/src/workflow/liberate/ArcanistLiberateWorkflow.php
@@ -202,6 +202,7 @@ EOTEXT
   }
 
   private function liberateWritePatches(array $results) {
+    assert_instances_of($results, 'ArcanistLintResult');
     $wrote = array();
 
     foreach ($results as $result) {