Also available at fake PR https://github.com/vallon/org-mode/pull/1

git fetch https://github.com/vallon/org-mode compat-for-flatten-tree

---
  lisp/org-src.el | 1 +
  1 file changed, 1 insertion(+)

diff --git a/lisp/org-src.el b/lisp/org-src.el
index 317682844..b8db7c128 100644
--- a/lisp/org-src.el
+++ b/lisp/org-src.el
@@ -40,6 +40,7 @@
  (require 'org-compat)
  (require 'org-keys)
  (require 'sh-script)
+(require 'compat)

  (declare-function org--get-expected-indentation "org" (element contentsp))
  (declare-function org-mode "org" ())
-- 
2.20.1