diff --git a/externals/jsonlint/src/Seld/JsonLint/JsonParser.php b/externals/jsonlint/src/Seld/JsonLint/JsonParser.php
--- a/externals/jsonlint/src/Seld/JsonLint/JsonParser.php
+++ b/externals/jsonlint/src/Seld/JsonLint/JsonParser.php
@@ -380,11 +380,7 @@
                 $errStr .= "Duplicate key: ".$tokens[$len][0];
                 throw new JsonLintParsingException($errStr);
             } elseif (($this->flags & self::ALLOW_DUPLICATE_KEYS) && array_key_exists($key, $tokens[$len-2])) {
-                $duplicateCount = 1;
-                do {
-                    $duplicateKey = $key . '.' . $duplicateCount++;
-                } while (array_key_exists($duplicateKey, $tokens[$len-2]));
-                $key = $duplicateKey;
+                // Forget about it...
             }
             $yyval->token[$key] = $tokens[$len][1];
             break;
diff --git a/src/parser/PhutilJSONParser.php b/src/parser/PhutilJSONParser.php
--- a/src/parser/PhutilJSONParser.php
+++ b/src/parser/PhutilJSONParser.php
@@ -8,6 +8,13 @@
  */
 final class PhutilJSONParser {
 
+  private $allowDuplicateKeys = false;
+
+  public function setAllowDuplicateKeys($allow_duplicate_keys) {
+    $this->allowDuplicateKeys = $allow_duplicate_keys;
+    return $this;
+  }
+
   public function parse($json) {
     $jsonlint_root = phutil_get_library_root('phutil').'/../externals/jsonlint';
     require_once($jsonlint_root.'/src/Seld/JsonLint/JsonParser.php');
@@ -17,17 +24,17 @@
 
     $parser = new JsonLintJsonParser();
     try {
-      $output = $parser->parse($json);
+      $output = $parser->parse($json, $this->getFlags());
     } catch (JsonLintParsingException $ex) {
       $details = $ex->getDetails();
       $message = preg_replace("/^Parse error .*\\^\n/s", '', $ex->getMessage());
 
       throw new PhutilJSONParserException(
           $message,
-          $details['loc']['last_line'],
-          $details['loc']['last_column'],
-          $details['token'],
-          $details['expected']);
+          idx(idx($details, 'loc', array()), 'last_line'),
+          idx(idx($details, 'loc', array()), 'last_column'),
+          idx($details, 'token'),
+          idx($details, 'expected'));
     }
 
     if (!is_array($output)) {
@@ -40,4 +47,16 @@
     return $output;
   }
 
+  private function getFlags() {
+    $flags = 0;
+
+    if ($this->allowDuplicateKeys) {
+      $flags |= JsonLintJsonParser::ALLOW_DUPLICATE_KEYS;
+    } else {
+      $flags |= JsonLintJsonParser::DETECT_KEY_CONFLICTS;
+    }
+
+    return $flags;
+  }
+
 }
diff --git a/src/parser/__tests__/PhutilJSONParserTestCase.php b/src/parser/__tests__/PhutilJSONParserTestCase.php
--- a/src/parser/__tests__/PhutilJSONParserTestCase.php
+++ b/src/parser/__tests__/PhutilJSONParserTestCase.php
@@ -86,4 +86,29 @@
     }
   }
 
+  public function testDuplicateKeys() {
+    $parser = new PhutilJSONParser();
+
+    $tests = array(
+      '{"foo": "bar", "foo": "baz"}' => array('foo' => 'baz'),
+    );
+
+    foreach ($tests as $input => $expect) {
+      $parser->setAllowDuplicateKeys(true);
+      $this->assertEqual(
+        $expect,
+        $parser->parse($input),
+        'Parsing JSON: '.$input);
+
+      $parser->setAllowDuplicateKeys(false);
+      $caught = null;
+      try {
+        $parser->parse($input);
+      } catch (Exception $ex) {
+        $caught = $ex;
+      }
+      $this->assertTrue($caught instanceof PhutilJSONParserException);
+    }
+  }
+
 }