diff --git a/arcanist/linter/IncludeGuardLinter.php b/arcanist/linter/IncludeGuardLinter.php
index 465d7bf5f..019fb5a6b 100644
--- a/arcanist/linter/IncludeGuardLinter.php
+++ b/arcanist/linter/IncludeGuardLinter.php
@@ -1,81 +1,83 @@
 <?php
 
 /**
  * Check the include guard matches the rules from the developer notes.
  */
 final class IncludeGuardLinter extends ArcanistLinter {
 
   const GUARD_PREFIX = 'BITCOIN_';
   const GUARD_SUFFIX = '_H';
 
   const INCLUDE_GUARD_INVALID = 1;
 
   const EXCEPTIONS = array(
     "src/test/fuzz/FuzzedDataProvider.h"
   );
 
   public function getInfoName() {
     return 'lint-include-guard';
   }
 
   public function getInfoDescription() {
     return pht('Check the include guard matches the rules from the developer '.
                'notes. ');
   }
 
   public function getLinterName() {
     return 'INCLUDE_GUARD';
   }
 
   public function getLinterConfigurationName() {
     return 'lint-include-guard';
   }
 
   public function getLintSeverityMap() {
     return array(
       self::INCLUDE_GUARD_INVALID => ArcanistLintSeverity::SEVERITY_ERROR,
     );
   }
 
   public function getLintNameMap() {
     return array(
       self::INCLUDE_GUARD_INVALID => pht('Include guard malformed or missing.'),
     );
   }
 
   public function lintPath($path) {
     // If file is in list of exceptions, let it go
     if (in_array($path, self::EXCEPTIONS)) {
       return;
     }
 
     $abspath = Filesystem::resolvePath($path, $this->getProjectRoot());
     $fileContent = Filesystem::readFile($abspath);
 
     $pathInfo = pathinfo($path);
 
     // Get the path components. They are relative to project root.
     $guard = explode('/', $pathInfo['dirname']);
     // Add the file name (without extension) to the path components.
     $guard[] = $pathInfo['filename'];
     // Skip the upper 'src' directory
     $guard = array_slice($guard, 1);
     // Join to a string using an underscore ('_') as the delimiter.
     $guard = implode('_', $guard);
+    // Replace any special char with an underscore.
+    $guard = preg_replace('/[^A-Za-z0-9]/', '_', $guard);
     // Transform the whole string to uppercase.
     $guard = strtoupper($guard);
     // Surround with prefix and suffix.
     $guard = self::GUARD_PREFIX.$guard.self::GUARD_SUFFIX;
 
     if (preg_match_all('@#(?:ifndef|define|endif //) '.$guard.'@',
       $fileContent) != 3) {
       return $this->raiseLintAtPath(
         self::INCLUDE_GUARD_INVALID,
         pht("Include guard is malformed or missing. Expected format:\n".
           "\t#ifndef %s\n".
           "\t#define %s\n".
           "\t...\n".
           "\t#endif // %s", $guard, $guard, $guard));
     }
   }
 }