diff --git a/src/error/__tests__/PhutilOpaqueEnvelopeTestCase.php b/src/error/__tests__/PhutilOpaqueEnvelopeTestCase.php
--- a/src/error/__tests__/PhutilOpaqueEnvelopeTestCase.php
+++ b/src/error/__tests__/PhutilOpaqueEnvelopeTestCase.php
@@ -8,9 +8,13 @@
     // the diff itself, and thus this source code. Since we look for the secret
     // in traces later on, split it apart here so that invocation via
     // "arc diff" doesn't create a false test failure.
-
     $secret = 'hunter'.'2';
 
+    // Also split apart this "signpost" value which we are not going to put in
+    // an envelope. We expect to be able to find it in the argument lists in
+    // stack traces, and don't want a false positive.
+    $signpost = 'shaman'.'3';
+
     $envelope = new PhutilOpaqueEnvelope($secret);
 
     $this->assertFalse(strpos(var_export($envelope, true), $secret));
@@ -24,23 +28,34 @@
     $this->assertFalse(strpos($dump, $secret));
 
     try {
-      $this->throwTrace($envelope);
+      $this->throwTrace($envelope, $signpost);
     } catch (Exception $ex) {
       $trace = $ex->getTrace();
-      $this->assertFalse(strpos(print_r($trace, true), $secret));
+
+      // NOTE: The entire trace may be very large and contain complex
+      // recursive datastructures. Look at only the last few frames: we expect
+      // to see the signpost value but not the secret.
+      $trace = array_slice($trace, 0, 2);
+      $trace = print_r($trace, true);
+
+      $this->assertTrue(strpos($trace, $signpost) !== false);
+      $this->assertFalse(strpos($trace, $secret));
     }
 
-    $backtrace = $this->getBacktrace($envelope);
+    $backtrace = $this->getBacktrace($envelope, $signpost);
+    $backtrace = array_slice($backtrace, 0, 2);
+
+    $this->assertTrue(strpos($trace, $signpost) !== false);
     $this->assertFalse(strpos(print_r($backtrace, true), $secret));
 
     $this->assertEqual($secret, $envelope->openEnvelope());
   }
 
-  private function throwTrace($v) {
+  private function throwTrace($v, $w) {
     throw new Exception('!');
   }
 
-  private function getBacktrace($v) {
+  private function getBacktrace($v, $w) {
     return debug_backtrace();
   }
 
diff --git a/src/parser/__tests__/PhutilTypeSpecTestCase.php b/src/parser/__tests__/PhutilTypeSpecTestCase.php
--- a/src/parser/__tests__/PhutilTypeSpecTestCase.php
+++ b/src/parser/__tests__/PhutilTypeSpecTestCase.php
@@ -150,8 +150,7 @@
     foreach ($map as $expect => $input) {
       $this->assertEqual(
         $expect,
-        PhutilTypeSpec::getTypeOf($input),
-        print_r($input, true));
+        PhutilTypeSpec::getTypeOf($input));
 
       PhutilTypeSpec::newFromString($expect)->check($input);
     }