diff --git a/src/__phutil_library_map__.php b/src/__phutil_library_map__.php
index b510bd5e..99c6f524 100644
--- a/src/__phutil_library_map__.php
+++ b/src/__phutil_library_map__.php
@@ -1,216 +1,218 @@
 <?php
 
 /**
  * This file is automatically generated. Use 'phutil_mapper.php' to rebuild it.
  * @generated
  */
 
 phutil_register_library_map(array(
   'class' =>
   array(
     'AbstractDirectedGraph' => 'utils/abstractgraph',
     'AbstractDirectedGraphTestCase' => 'utils/abstractgraph/__tests__',
     'BaseHTTPFuture' => 'future/http/base',
     'CommandException' => 'future/exec',
     'ConduitClient' => 'conduit/client',
     'ConduitClientException' => 'conduit/client',
     'ConduitFuture' => 'conduit/client',
     'ExecFuture' => 'future/exec',
     'FileFinder' => 'filesystem/filefinder',
     'FileList' => 'filesystem/filelist',
     'Filesystem' => 'filesystem',
     'FilesystemException' => 'filesystem',
     'Future' => 'future',
     'FutureIterator' => 'future',
     'FutureProxy' => 'future/proxy',
     'HTTPFuture' => 'future/http/http',
     'HTTPFutureResponseStatus' => 'future/http/status/base',
     'HTTPFutureResponseStatusCURL' => 'future/http/status/curl',
     'HTTPFutureResponseStatusHTTP' => 'future/http/status/http',
     'HTTPFutureResponseStatusParse' => 'future/http/status/parse',
     'HTTPFutureResponseStatusTransport' => 'future/http/status/transport',
     'HTTPSFuture' => 'future/http/https',
     'ImmediateFuture' => 'future/immediate',
+    'JSONReadableSerializerTestCase' => 'parser/json/__tests__',
     'LinesOfALargeFile' => 'filesystem/linesofalargefile',
     'MFilterTestHelper' => 'utils/__tests__',
     'PhutilConsoleFormatter' => 'console',
     'PhutilConsoleStdinNotInteractiveException' => 'console/exception',
     'PhutilDaemon' => 'daemon/base',
     'PhutilDaemonOverseer' => 'daemon/overseer',
     'PhutilDefaultSyntaxHighlighter' => 'markup/syntax/highlighter/default',
     'PhutilDefaultSyntaxHighlighterEngine' => 'markup/syntax/engine/default',
     'PhutilDefaultSyntaxHighlighterEnginePygmentsFuture' => 'markup/syntax/highlighter/pygments/future',
     'PhutilDefaultSyntaxHighlighterEngineTestCase' => 'markup/syntax/engine/default/__tests__',
     'PhutilDivinerSyntaxHighlighter' => 'markup/syntax/highlighter/diviner',
     'PhutilDocblockParser' => 'parser/docblock',
     'PhutilDocblockParserTestCase' => 'parser/docblock/__tests__',
     'PhutilEmailAddress' => 'parser/emailaddress',
     'PhutilEmailAddressTestCase' => 'parser/emailaddress/__tests__',
     'PhutilErrorHandler' => 'error',
     'PhutilEvent' => 'events/event',
     'PhutilEventConstants' => 'events/constant/base',
     'PhutilEventEngine' => 'events/engine',
     'PhutilEventListener' => 'events/listener',
     'PhutilEventType' => 'events/constant/type',
     'PhutilExcessiveServiceCallsDaemon' => 'daemon/torture/excessiveservicecalls',
     'PhutilFatalDaemon' => 'daemon/torture/fatal',
     'PhutilHangForeverDaemon' => 'daemon/torture/hangforever',
     'PhutilInteractiveEditor' => 'console/editor',
     'PhutilJSON' => 'parser/json',
     'PhutilMarkupEngine' => 'markup/engine',
     'PhutilMissingSymbolException' => 'symbols/exception/missing',
     'PhutilNiceDaemon' => 'daemon/torture/nice',
     'PhutilProcessGroupDaemon' => 'daemon/torture/processgroup',
     'PhutilPygmentsSyntaxHighlighter' => 'markup/syntax/highlighter/pygments',
     'PhutilRainbowSyntaxHighlighter' => 'markup/syntax/highlighter/rainbow',
     'PhutilReadableSerializer' => 'readableserializer',
     'PhutilRemarkupBlockStorage' => 'markup/engine/remarkup/blockstorage',
     'PhutilRemarkupEngine' => 'markup/engine/remarkup',
     'PhutilRemarkupEngineBlockRule' => 'markup/engine/remarkup/blockrule/base',
     'PhutilRemarkupEngineRemarkupCodeBlockRule' => 'markup/engine/remarkup/blockrule/remarkupcode',
     'PhutilRemarkupEngineRemarkupDefaultBlockRule' => 'markup/engine/remarkup/blockrule/remarkupdefault',
     'PhutilRemarkupEngineRemarkupHeaderBlockRule' => 'markup/engine/remarkup/blockrule/remarkupheader',
     'PhutilRemarkupEngineRemarkupInlineBlockRule' => 'markup/engine/remarkup/blockrule/remarkupinline',
     'PhutilRemarkupEngineRemarkupListBlockRule' => 'markup/engine/remarkup/blockrule/remarkuplist',
     'PhutilRemarkupEngineRemarkupNoteBlockRule' => 'markup/engine/remarkup/blockrule/remarkupnote',
     'PhutilRemarkupEngineRemarkupQuotesBlockRule' => 'markup/engine/remarkup/blockrule/remarkupquotes',
     'PhutilRemarkupEngineTestCase' => 'markup/engine/remarkup/__tests__',
     'PhutilRemarkupRule' => 'markup/engine/remarkup/markuprule/base',
     'PhutilRemarkupRuleBold' => 'markup/engine/remarkup/markuprule/bold',
     'PhutilRemarkupRuleEscapeHTML' => 'markup/engine/remarkup/markuprule/escapehtml',
     'PhutilRemarkupRuleEscapeRemarkup' => 'markup/engine/remarkup/markuprule/escaperemarkup',
     'PhutilRemarkupRuleHyperlink' => 'markup/engine/remarkup/markuprule/hyperlink',
     'PhutilRemarkupRuleItalic' => 'markup/engine/remarkup/markuprule/italics',
     'PhutilRemarkupRuleLinebreaks' => 'markup/engine/remarkup/markuprule/linebreaks',
     'PhutilRemarkupRuleMonospace' => 'markup/engine/remarkup/markuprule/monospace',
     'PhutilSaturateStdoutDaemon' => 'daemon/torture/saturatestdout',
     'PhutilServiceProfiler' => 'serviceprofiler',
     'PhutilSymbolLoader' => 'symbols',
     'PhutilSyntaxHighlighter' => 'markup/syntax/highlighter/base',
     'PhutilSyntaxHighlighterEngine' => 'markup/syntax/engine/base',
     'PhutilTortureTestDaemon' => 'daemon/torture/base',
     'PhutilURI' => 'parser/uri',
     'PhutilURITestCase' => 'parser/uri/__tests__',
     'PhutilUTF8TestCase' => 'utils/__tests__',
     'PhutilUtilsTestCase' => 'utils/__tests__',
     'PhutilXHPASTSyntaxHighlighter' => 'markup/syntax/highlighter/xhpast',
     'PhutilXHPASTSyntaxHighlighterTestCase' => 'markup/syntax/highlighter/xhpast/__tests__',
     'TempFile' => 'filesystem/tempfile',
     'TestAbstractDirectedGraph' => 'utils/abstractgraph/__tests__',
     'XHPASTNode' => 'parser/xhpast/api/node',
     'XHPASTNodeList' => 'parser/xhpast/api/list',
     'XHPASTSyntaxErrorException' => 'parser/xhpast/api/exception',
     'XHPASTToken' => 'parser/xhpast/api/token',
     'XHPASTTree' => 'parser/xhpast/api/tree',
     'XHPASTTreeTestCase' => 'parser/xhpast/api/tree/__tests__',
   ),
   'function' =>
   array(
     'Futures' => 'future',
     'array_mergev' => 'utils',
     'array_select_keys' => 'utils',
     'coalesce' => 'utils',
     'csprintf' => 'xsprintf/csprintf',
     'exec_manual' => 'future/exec',
     'execx' => 'future/exec',
     'head' => 'utils',
     'id' => 'utils',
     'idx' => 'utils',
     'ifilter' => 'utils',
     'igroup' => 'utils',
     'ipull' => 'utils',
     'isort' => 'utils',
     'jsprintf' => 'xsprintf/jsprintf',
     'mfilter' => 'utils',
     'mgroup' => 'utils',
     'mpull' => 'utils',
     'msort' => 'utils',
     'newv' => 'utils',
     'nonempty' => 'utils',
     'phlog' => 'error',
     'phutil_console_confirm' => 'console',
     'phutil_console_format' => 'console',
     'phutil_console_prompt' => 'console',
     'phutil_console_require_tty' => 'console',
     'phutil_console_wrap' => 'console',
     'phutil_deprecated' => 'moduleutils',
     'phutil_error_listener_example' => 'error',
     'phutil_escape_html' => 'markup',
     'phutil_escape_uri' => 'markup',
     'phutil_get_library_name_for_root' => 'moduleutils',
     'phutil_get_library_root' => 'moduleutils',
     'phutil_get_library_root_for_path' => 'moduleutils',
     'phutil_is_utf8' => 'utils',
     'phutil_passthru' => 'future/exec',
     'phutil_render_tag' => 'markup',
     'phutil_utf8_shorten' => 'utils',
     'phutil_utf8_strlen' => 'utils',
     'phutil_utf8ize' => 'utils',
     'phutil_utf8v' => 'utils',
     'vcsprintf' => 'xsprintf/csprintf',
     'vjsprintf' => 'xsprintf/jsprintf',
     'xhp_parser_node_constants' => 'parser/xhpast/constants',
     'xhpast_get_binary_path' => 'parser/xhpast/bin',
     'xhpast_get_build_instructions' => 'parser/xhpast/bin',
     'xhpast_get_parser_future' => 'parser/xhpast/bin',
     'xhpast_is_available' => 'parser/xhpast/bin',
     'xhpast_parser_token_constants' => 'parser/xhpast/constants',
     'xsprintf' => 'xsprintf',
     'xsprintf_callback_example' => 'xsprintf',
     'xsprintf_command' => 'xsprintf/csprintf',
     'xsprintf_javascript' => 'xsprintf/jsprintf',
   ),
   'requires_class' =>
   array(
     'AbstractDirectedGraphTestCase' => 'ArcanistPhutilTestCase',
     'BaseHTTPFuture' => 'Future',
     'ConduitFuture' => 'FutureProxy',
     'ExecFuture' => 'Future',
     'FutureProxy' => 'Future',
     'HTTPFuture' => 'BaseHTTPFuture',
     'HTTPFutureResponseStatusCURL' => 'HTTPFutureResponseStatus',
     'HTTPFutureResponseStatusHTTP' => 'HTTPFutureResponseStatus',
     'HTTPFutureResponseStatusParse' => 'HTTPFutureResponseStatus',
     'HTTPFutureResponseStatusTransport' => 'HTTPFutureResponseStatus',
     'HTTPSFuture' => 'BaseHTTPFuture',
     'ImmediateFuture' => 'Future',
+    'JSONReadableSerializerTestCase' => 'ArcanistPhutilTestCase',
     'PhutilDefaultSyntaxHighlighterEngine' => 'PhutilSyntaxHighlighterEngine',
     'PhutilDefaultSyntaxHighlighterEnginePygmentsFuture' => 'FutureProxy',
     'PhutilDefaultSyntaxHighlighterEngineTestCase' => 'ArcanistPhutilTestCase',
     'PhutilDocblockParserTestCase' => 'ArcanistPhutilTestCase',
     'PhutilEmailAddressTestCase' => 'ArcanistPhutilTestCase',
     'PhutilEventType' => 'PhutilEventConstants',
     'PhutilExcessiveServiceCallsDaemon' => 'PhutilTortureTestDaemon',
     'PhutilFatalDaemon' => 'PhutilTortureTestDaemon',
     'PhutilHangForeverDaemon' => 'PhutilTortureTestDaemon',
     'PhutilNiceDaemon' => 'PhutilTortureTestDaemon',
     'PhutilProcessGroupDaemon' => 'PhutilTortureTestDaemon',
     'PhutilRemarkupEngine' => 'PhutilMarkupEngine',
     'PhutilRemarkupEngineRemarkupCodeBlockRule' => 'PhutilRemarkupEngineBlockRule',
     'PhutilRemarkupEngineRemarkupDefaultBlockRule' => 'PhutilRemarkupEngineBlockRule',
     'PhutilRemarkupEngineRemarkupHeaderBlockRule' => 'PhutilRemarkupEngineBlockRule',
     'PhutilRemarkupEngineRemarkupInlineBlockRule' => 'PhutilRemarkupEngineBlockRule',
     'PhutilRemarkupEngineRemarkupListBlockRule' => 'PhutilRemarkupEngineBlockRule',
     'PhutilRemarkupEngineRemarkupNoteBlockRule' => 'PhutilRemarkupEngineBlockRule',
     'PhutilRemarkupEngineRemarkupQuotesBlockRule' => 'PhutilRemarkupEngineBlockRule',
     'PhutilRemarkupEngineTestCase' => 'ArcanistPhutilTestCase',
     'PhutilRemarkupRuleBold' => 'PhutilRemarkupRule',
     'PhutilRemarkupRuleEscapeHTML' => 'PhutilRemarkupRule',
     'PhutilRemarkupRuleEscapeRemarkup' => 'PhutilRemarkupRule',
     'PhutilRemarkupRuleHyperlink' => 'PhutilRemarkupRule',
     'PhutilRemarkupRuleItalic' => 'PhutilRemarkupRule',
     'PhutilRemarkupRuleLinebreaks' => 'PhutilRemarkupRule',
     'PhutilRemarkupRuleMonospace' => 'PhutilRemarkupRule',
     'PhutilSaturateStdoutDaemon' => 'PhutilTortureTestDaemon',
     'PhutilTortureTestDaemon' => 'PhutilDaemon',
     'PhutilURITestCase' => 'ArcanistPhutilTestCase',
     'PhutilUTF8TestCase' => 'ArcanistPhutilTestCase',
     'PhutilUtilsTestCase' => 'ArcanistPhutilTestCase',
     'PhutilXHPASTSyntaxHighlighterTestCase' => 'ArcanistPhutilTestCase',
     'TestAbstractDirectedGraph' => 'AbstractDirectedGraph',
     'XHPASTTreeTestCase' => 'ArcanistPhutilTestCase',
   ),
   'requires_interface' =>
   array(
   ),
 ));
diff --git a/src/parser/json/PhutilJSON.php b/src/parser/json/PhutilJSON.php
index b0fbcf05..487a92bd 100644
--- a/src/parser/json/PhutilJSON.php
+++ b/src/parser/json/PhutilJSON.php
@@ -1,106 +1,106 @@
 <?php
 
 /*
  * Copyright 2011 Facebook, Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  *   http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
 
 /**
  * Utilities for wrangling JSON.
  *
  */
 final class PhutilJSON {
 
   /**
    * Encode an object in JSON and pretty-print it.
    *
    * @param   dict    An object to encode in JSON.
    * @return  string  Pretty-printed object representation.
    */
   public function encodeFormatted(array $object) {
     return $this->encodeFormattedObject($object, 0)."\n";
   }
 
   private function encodeFormattedObject($object, $depth) {
     if (empty($object)) {
       return '{}';
     }
 
     $pre = $this->getIndent($depth);
     $key_pre = $this->getIndent($depth + 1);
     $keys = array();
     $vals = array();
     $max = 0;
     foreach ($object as $key => $val) {
       $ekey = $this->encodeFormattedValue((string)$key, 0);
       $max = max($max, strlen($ekey));
       $keys[] = $ekey;
       $vals[] = $this->encodeFormattedValue($val, $depth + 1);
     }
     $key_lines = array();
     foreach ($keys as $k => $key) {
       $key_lines[] = $key_pre.str_pad($key, $max).' : '.$vals[$k];
     }
     $key_lines = implode(",\n", $key_lines);
 
     $out  = "{\n";
     $out .= $key_lines;
     $out .= "\n";
     $out .= $pre.'}';
 
     return $out;
   }
 
   private function encodeFormattedArray($array, $depth) {
     if (empty($array)) {
       return '[]';
     }
 
     $pre = $this->getIndent($depth);
     $val_pre = $this->getIndent($depth + 1);
 
     $vals = array();
     foreach ($array as $val) {
       $vals[] = $val_pre.$this->encodeFormattedValue($val, $depth + 1);
     }
     $val_lines = implode(",\n", $vals);
 
     $out  = "[\n";
     $out .= $val_lines;
     $out .= "\n";
     $out .= $pre.']';
 
     return $out;
   }
 
   private function encodeFormattedValue($value, $depth) {
     if (is_array($value)) {
-      if (array_keys($value) === range(0, count($value) - 1)) {
+      if (empty($value) || array_keys($value) === range(0, count($value) - 1)) {
         return $this->encodeFormattedArray($value, $depth);
       } else {
         return $this->encodeFormattedObject($value, $depth);
       }
     } else {
       return json_encode($value);
     }
   }
 
   private function getIndent($depth) {
     if (!$depth) {
       return '';
     } else {
       return str_repeat('  ', $depth);
     }
   }
 }
diff --git a/src/parser/json/__tests__/JSONReadableSerializerTestCase.php b/src/parser/json/__tests__/JSONReadableSerializerTestCase.php
new file mode 100644
index 00000000..25d4e103
--- /dev/null
+++ b/src/parser/json/__tests__/JSONReadableSerializerTestCase.php
@@ -0,0 +1,37 @@
+<?php
+
+/*
+ * Copyright 2011 Facebook, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+class JSONReadableSerializerTestCase extends ArcanistPhutilTestCase {
+
+  public function testEmptyArrayEncoding() {
+    $serializer = new PhutilJSON();
+
+    $expect = <<<EOJSON
+{
+  "x" : []
+}
+
+EOJSON;
+
+    $this->assertEqual(
+      $expect,
+      $serializer->encodeFormatted(array('x' => array())),
+      'Empty arrays should serialize as [], not {}.');
+  }
+
+}
diff --git a/src/parser/json/__tests__/__init__.php b/src/parser/json/__tests__/__init__.php
new file mode 100644
index 00000000..043158dc
--- /dev/null
+++ b/src/parser/json/__tests__/__init__.php
@@ -0,0 +1,14 @@
+<?php
+/**
+ * This file is automatically generated. Lint this module to rebuild it.
+ * @generated
+ */
+
+
+
+phutil_require_module('arcanist', 'unit/engine/phutil/testcase');
+
+phutil_require_module('phutil', 'parser/json');
+
+
+phutil_require_source('JSONReadableSerializerTestCase.php');