diff --git a/src/markup/engine/remarkup/blockrule/PhutilRemarkupCodeBlockRule.php b/src/markup/engine/remarkup/blockrule/PhutilRemarkupCodeBlockRule.php
--- a/src/markup/engine/remarkup/blockrule/PhutilRemarkupCodeBlockRule.php
+++ b/src/markup/engine/remarkup/blockrule/PhutilRemarkupCodeBlockRule.php
@@ -120,11 +120,18 @@
       // If the user hasn't specified "lang=..." explicitly, try to guess the
       // language. If we fail, fall back to configured defaults.
       $lang = PhutilLanguageGuesser::guessLanguage($text);
+
+      if (!$lang && $options['name']) {
+        $lang = $this->getHighlighterEngine()
+          ->getLanguageFromFilename($options['name']);
+      }
+
       if (!$lang) {
         $lang = nonempty(
           $this->getEngine()->getConfig('phutil.codeblock.language-default'),
           'text');
       }
+
       $options['lang'] = $lang;
     }
 
@@ -230,14 +237,6 @@
         .'em; overflow: auto;';
     }
 
-    $engine = $this->getEngine()->getConfig('syntax-highlighter.engine');
-    if (!$engine) {
-      $engine = 'PhutilDefaultSyntaxHighlighterEngine';
-    }
-    $engine = newv($engine, array());
-    $engine->setConfig(
-      'pygments.enabled',
-      $this->getEngine()->getConfig('pygments.enabled'));
     return phutil_tag(
       'pre',
       array(
@@ -246,7 +245,26 @@
       ),
       PhutilSafeHTML::applyFunction(
         'rtrim',
-        $engine->highlightSource($options['lang'], $text)));
+        $this->getHighlighterEngine()
+          ->highlightSource($options['lang'], $text)));
+  }
+
+  private function getHighlighterEngine() {
+    $engine = $this->getEngine()->getConfig('syntax-highlighter.engine');
+
+    if (!$engine) {
+      $engine = 'PhutilDefaultSyntaxHighlighterEngine';
+    }
+
+    $engine = newv($engine, array());
+    $engine->setConfig(
+      'pygments.enabled',
+      $this->getEngine()->getConfig('pygments.enabled'));
+    $engine->setConfig(
+      'filename.map',
+      $this->getEngine()->getConfig('filename.map'));
+
+    return $engine;
   }
 
 }