diff --git a/gdscript-syntax.el b/gdscript-syntax.el
index 5a78010..21993c2 100644
--- a/gdscript-syntax.el
+++ b/gdscript-syntax.el
@@ -59,8 +59,8 @@
 (defvar gdscript-font-lock `((,(gdscript-syntax-regex-maker gdscript-keywords)
                               1
                               font-lock-keyword-face)
-                             (,(gdscript-syntax-regex-maker (cl-concatenate 'list gdscript-built-in-constants
-                                                                            gdscript-built-in-types gdscript-built-in-functions))
+                             (,(gdscript-syntax-regex-maker (append gdscript-built-in-constants
+                                                                    gdscript-built-in-types gdscript-built-in-functions))
                               1
                               font-lock-builtin-face)
                              (,(gdscript-syntax-regex-maker gdscript-built-in-classes)