diff --git a/Fltk/spherePositionWidget.h b/Fltk/spherePositionWidget.h
index 094d40fb2128cb594dc4f89b40b7b49402ba4a9b..5a5c959673c52f288e71e5389f7acdd45b2752ec 100644
--- a/Fltk/spherePositionWidget.h
+++ b/Fltk/spherePositionWidget.h
@@ -9,6 +9,7 @@
 #include <math.h>
 #include <FL/Fl_Widget.H>
 #include <FL/fl_draw.H>
+#include <FL/Fl.H>
 
 // A small 2D widget to set the coordinates of a point on the unit
 // sphere.