diff --git a/Source/FLTKDialog/FLTKDialog.cxx b/Source/FLTKDialog/FLTKDialog.cxx
index 8e5935306..dedb2e414 100644
--- a/Source/FLTKDialog/FLTKDialog.cxx
+++ b/Source/FLTKDialog/FLTKDialog.cxx
@@ -16,7 +16,7 @@
 =========================================================================*/
 
 #include "CMakeSetupGUIImplementation.h"
-#include "FL/Fl.h"
+#include "FL/Fl.H"
 #include "FL/fl_ask.H"
 
 int main(int argc, char * argv[] )