diff --git a/src/infrastructure/markup/blockrule/PhutilRemarkupCodeBlockRule.php b/src/infrastructure/markup/blockrule/PhutilRemarkupCodeBlockRule.php
--- a/src/infrastructure/markup/blockrule/PhutilRemarkupCodeBlockRule.php
+++ b/src/infrastructure/markup/blockrule/PhutilRemarkupCodeBlockRule.php
@@ -63,8 +63,11 @@
       'lines'           => null,
     );
 
+    // The options after the first backticks.
+    $first_line = head($lines);
+
     $parser = new PhutilSimpleOptions();
-    $custom = $parser->parse(head($lines));
+    $custom = $parser->parse($first_line);
     if ($custom) {
       $valid = true;
       foreach ($custom as $key => $value) {
@@ -79,6 +82,16 @@
       }
     }
 
+    // Very early, eventually parse the language expressed
+    // in the very first line, just after the first backticks.
+    // But, in case, let's remove that line.
+    if (empty($options['lang']) && $first_line) {
+      if ($this->isProbablyLanguageCode($first_line)) {
+        $options['lang'] = $first_line;
+        array_shift($lines);
+      }
+    }
+
     // Normalize the text back to a 0-level indent.
     $min_indent = 80;
     foreach ($lines as $line) {
@@ -249,4 +262,19 @@
         $engine->highlightSource($options['lang'], $text)));
   }
 
+  /**
+   * Check if a string is very probably a language code
+   * recognized by the Pygments library (or maybe others).
+   *
+   * @param string $s
+   * @return bool
+   */
+  private function isProbablyLanguageCode($s) {
+    // If not already specified, try to match the language from: ```thelang
+    // This regex was manually and empirically crafted to try to match
+    // all the available stuff from Pygments.
+    // https://pygments.org/languages/
+    return preg_match('/^[a-z0-9\-\+\#\/]+$/', $s);
+  }
+
 }