diff --git a/src/__phutil_library_map__.php b/src/__phutil_library_map__.php
--- a/src/__phutil_library_map__.php
+++ b/src/__phutil_library_map__.php
@@ -2373,6 +2373,7 @@
     'PhabricatorConfigPageView' => 'applications/config/view/PhabricatorConfigPageView.php',
     'PhabricatorConfigProxySource' => 'infrastructure/env/PhabricatorConfigProxySource.php',
     'PhabricatorConfigPurgeCacheController' => 'applications/config/controller/PhabricatorConfigPurgeCacheController.php',
+    'PhabricatorConfigRegexOptionType' => 'applications/config/custom/PhabricatorConfigRegexOptionType.php',
     'PhabricatorConfigRequestExceptionHandlerModule' => 'applications/config/module/PhabricatorConfigRequestExceptionHandlerModule.php',
     'PhabricatorConfigResponse' => 'applications/config/response/PhabricatorConfigResponse.php',
     'PhabricatorConfigSchemaQuery' => 'applications/config/schema/PhabricatorConfigSchemaQuery.php',
@@ -7473,6 +7474,7 @@
     'PhabricatorConfigPageView' => 'AphrontTagView',
     'PhabricatorConfigProxySource' => 'PhabricatorConfigSource',
     'PhabricatorConfigPurgeCacheController' => 'PhabricatorConfigController',
+    'PhabricatorConfigRegexOptionType' => 'PhabricatorConfigJSONOptionType',
     'PhabricatorConfigRequestExceptionHandlerModule' => 'PhabricatorConfigModule',
     'PhabricatorConfigResponse' => 'AphrontStandaloneHTMLResponse',
     'PhabricatorConfigSchemaQuery' => 'Phobject',
diff --git a/src/applications/config/custom/PhabricatorConfigRegexOptionType.php b/src/applications/config/custom/PhabricatorConfigRegexOptionType.php
new file mode 100644
--- /dev/null
+++ b/src/applications/config/custom/PhabricatorConfigRegexOptionType.php
@@ -0,0 +1,18 @@
+<?php
+
+class PhabricatorConfigRegexOptionType
+  extends PhabricatorConfigJSONOptionType {
+
+  public function validateOption(PhabricatorConfigOption $option, $value) {
+    foreach ($value as $pattern => $spec) {
+      $ok = preg_match($pattern, '');
+      if ($ok === false) {
+        throw new Exception(
+          pht(
+            'The following regex is malformed and cannot be used: %s',
+            $pattern));
+      }
+    }
+  }
+
+}
diff --git a/src/applications/config/option/PhabricatorSyntaxHighlightingConfigOptions.php b/src/applications/config/option/PhabricatorSyntaxHighlightingConfigOptions.php
--- a/src/applications/config/option/PhabricatorSyntaxHighlightingConfigOptions.php
+++ b/src/applications/config/option/PhabricatorSyntaxHighlightingConfigOptions.php
@@ -120,7 +120,7 @@
             'this is where that list is defined.')),
       $this->newOption(
         'syntax.filemap',
-        'wild',
+        'custom:PhabricatorConfigRegexOptionType',
         array(
           '@\.arcconfig$@' => 'js',
           '@\.arclint$@' => 'js',
@@ -138,12 +138,14 @@
             'be tested against the filename. They should map to either an '.
             'explicit language as a string value, or a numeric index into '.
             'the captured groups as an integer.'))
-      ->addExample('{"@\\.xyz$@": "php"}', pht('Highlight %s as PHP.', '*.xyz'))
       ->addExample(
-        '{"@/httpd\\.conf@": "apacheconf"}',
+        '{"@\\\.xyz$@": "php"}',
+        pht('Highlight %s as PHP.', '*.xyz'))
+      ->addExample(
+        '{"@/httpd\\\.conf@": "apacheconf"}',
         pht('Highlight httpd.conf as "apacheconf".'))
       ->addExample(
-        '{"@\\.([^.]+)\\.bak$@": 1}',
+        '{"@\\\.([^.]+)\\\.bak$@": 1}',
         pht(
           "Treat all '*.x.bak' file as '.x'. NOTE: We map to capturing group ".
           "1 by specifying the mapping as '1'")),