1 files changed, 1 insertions, 0 deletions
diff --git a/FL/mac.H b/FL/mac.H
index c2e6d54e5..f00fe240d 100644
--- a/FL/mac.H
+++ b/FL/mac.H
@@ -33,6 +33,7 @@ typedef class FLWindow *Window; // pointer to the FLWindow objective-c class
 #endif // __OBJC__
 
 #include <FL/Fl_System_Driver.H>
+#include <FL/Fl_Widget.H> // for Fl_Callback
 
 #if !(defined(FL_LIBRARY) || defined(FL_INTERNALS)) // this part is used when compiling an application program