diff --git a/src/main/php/xp/lambda/AwsRunner.class.php b/src/main/php/xp/lambda/AwsRunner.class.php
index 151fe3c..9f158a9 100755
--- a/src/main/php/xp/lambda/AwsRunner.class.php
+++ b/src/main/php/xp/lambda/AwsRunner.class.php
@@ -49,50 +49,31 @@ private static function endpoint($environment, $path) {
     return $c;
   }
 
-  /**
-   * Reads a value from the given input stream
-   *
-   * @param  io.streams.InputStream
-   * @return var
-   */
-  private static function read($in) {
-    return Json::read(new StreamInput($in));
-  }
-
-  /**
-   * Marshals a value 
-   *
-   * @param  var $value
-   * @return string
-   */
-  private static function value($value) {
-    return Json::of($value);
-  }
-
   /**
    * Marshals an error according to the AWS specification.
    *
    * @param  Throwable $e
-   * @return string
+   * @return [:var]
    */
-  private static function error($e) {
+  public static function error($e) {
     $error= ['errorMessage' => $e->getMessage(), 'errorType' => nameof($e), 'stackTrace' => []];
 
     $t= XPException::wrap($e);
     do {
+      $error['stackTrace'][]= $t->compoundMessage();
       foreach ($t->getStackTrace() as $e) {
         $error['stackTrace'][]= sprintf(
           '%s::%s(...) (line %d of %s)%s',
           strtr($e->class, '\\', '.') ?: '<main>',
           $e->method,
           $e->line,
-          basename($e->file),
+          $e->file ? basename($e->file) : '',
           $e->message ? ' - '.$e->message : ''
         );
       }
     } while ($t= $t->getCause());
 
-    return Json::of($error);
+    return $error;
   }
 
   /**
@@ -109,7 +90,7 @@ public static function main($args) {
       $lambda= self::handler($environment, Console::$out)->lambda();
     } catch (Throwable $t) {
       self::endpoint($environment, 'init/error')->post(
-        new RequestData(self::error($t)),
+        new RequestData(Json::of(self::error($t))),
         ['Content-Type' => 'application/json']
       );
       return 1;
@@ -126,17 +107,16 @@ public static function main($args) {
 
       $context= new Context($r->headers(), $environment);
       try {
-        $event= 0 === $context->payloadLength ? null : self::read($r->in());
-
+        $event= 0 === $context->payloadLength ? null : Json::read(new StreamInput($r->in()));
         $type= 'response';
-        $response= self::value($lambda($event, $context));
+        $response= $lambda($event, $context);
       } catch (Throwable $t) {
         $type= 'error';
         $response= self::error($t);
       }
 
       self::endpoint($environment, "invocation/{$context->awsRequestId}/{$type}")->post(
-        new RequestData($response),
+        new RequestData(Json::of($response)),
         ['Content-Type' => 'application/json']
       );
     } while (true);
diff --git a/src/test/php/com/amazon/aws/lambda/unittest/ExceptionTest.class.php b/src/test/php/com/amazon/aws/lambda/unittest/ExceptionTest.class.php
new file mode 100644
index 0000000..5bc09a9
--- /dev/null
+++ b/src/test/php/com/amazon/aws/lambda/unittest/ExceptionTest.class.php
@@ -0,0 +1,40 @@
+<?php namespace com\amazon\aws\lambda\unittest;
+
+use lang\{IllegalArgumentException, IllegalStateException};
+use unittest\{Assert, Test};
+use xp\lambda\AwsRunner;
+
+class ExceptionTest {
+
+  #[Test]
+  public function includes_errorMessage() {
+    Assert::equals(
+      'Test',
+      AwsRunner::error(new IllegalArgumentException('Test'))['errorMessage']
+    );
+  }
+
+  #[Test]
+  public function includes_errorType() {
+    Assert::equals(
+      'lang.IllegalArgumentException',
+      AwsRunner::error(new IllegalArgumentException('Test'))['errorType']
+    );
+  }
+
+  #[Test]
+  public function includes_stackTrace() {
+    Assert::true(in_array(
+      'Exception lang.IllegalArgumentException (Test)',
+      AwsRunner::error(new IllegalArgumentException('Test'))['stackTrace']
+    ));
+  }
+
+  #[Test]
+  public function includes_cause() {
+    Assert::true(in_array(
+      'Exception lang.IllegalStateException (Cause)',
+      AwsRunner::error(new IllegalArgumentException('Test', new IllegalStateException('Cause')))['stackTrace']
+    ));
+  }
+}
\ No newline at end of file