diff --git a/phpBB/phpbb/template/twig/lexer.php b/phpBB/phpbb/template/twig/lexer.php
index 8b72a06642..16a693cd7c 100644
--- a/phpBB/phpbb/template/twig/lexer.php
+++ b/phpBB/phpbb/template/twig/lexer.php
@@ -75,7 +75,7 @@ class phpbb_template_twig_lexer extends Twig_Lexer
 
 		// Fix tokens that may have inline variables (e.g. <!-- DEFINE $TEST = '{FOO}')
 		$code = $this->fix_inline_variable_tokens(array(
-			'DEFINE \$[a-zA-Z0-9]+ =',
+			'DEFINE \$[a-zA-Z0-9_]+ =',
 			'INCLUDE',
 			'INCLUDEPHP',
 			'INCLUDEJS',