diff --git a/FL/Fl_Flowpack.H b/FL/Fl_Flowpack.H
index c011a93..fe3980e 100644
--- a/FL/Fl_Flowpack.H
+++ b/FL/Fl_Flowpack.H
@@ -20,6 +20,7 @@
 #pragma once
 
 #include <FL/Fl_Group.H>
+#include <FL/Fl_Pack.H>
 
 class Fl_Flowpack : public Fl_Group
 {