diff --git a/lisp/ob-forth.el b/lisp/ob-forth.el
index 85be0de3b..cc2795a4f 100644
--- a/lisp/ob-forth.el
+++ b/lisp/ob-forth.el
@@ -34,6 +34,8 @@
 ;;; Code:
 (require 'ob)
 
+(declare-function forth-proc "ext:gforth" ())
+
 (defvar org-babel-default-header-args:forth '((:session . "yes"))
   "Default header arguments for forth code blocks.")