diff --git a/FL/Fl_Pixmap.H b/FL/Fl_Pixmap.H
index f920961e8..a33846ad6 100644
--- a/FL/Fl_Pixmap.H
+++ b/FL/Fl_Pixmap.H
@@ -46,7 +46,7 @@ class FL_EXPORT Fl_Pixmap : public Fl_Image {
   void copy_data();
   void delete_data();
   void set_data(const char * const *p);
-  int prepare(int XP, int YP, int WP, int HP, int cx, int cy,
+  int prepare(int XP, int YP, int WP, int HP, int &cx, int &cy,
 			 int &X, int &Y, int &W, int &H);
 
   protected:
diff --git a/src/Fl_Pixmap.cxx b/src/Fl_Pixmap.cxx
index 7d7fa65c7..31b90e5e3 100644
--- a/src/Fl_Pixmap.cxx
+++ b/src/Fl_Pixmap.cxx
@@ -92,7 +92,7 @@ static int start(Fl_Pixmap *pxm, int XP, int YP, int WP, int HP, int w, int h, i
   return 0;
 }
 
-int Fl_Pixmap::prepare(int XP, int YP, int WP, int HP, int cx, int cy,
+int Fl_Pixmap::prepare(int XP, int YP, int WP, int HP, int &cx, int &cy,
 			   int &X, int &Y, int &W, int &H) {
   if (w() < 0) measure();
   int code = start(this, XP, YP, WP, HP, w(), h(), cx, cy, X, Y, W, H);