diff --git a/CHANGES b/CHANGES
index 1f8cd1aff..5d93cf575 100644
--- a/CHANGES
+++ b/CHANGES
@@ -92,6 +92,8 @@ CHANGES IN FLTK 1.3.4					RELEASED: ??? ?? 2016
 
 	Bug fixes
 
+	- Fixed valgrind warning (uninitialized variable) in Fl_Window.
+	  Visible only with FLTK_ABI_VERSION >= 10303, since FLTK 1.3.3.
 	- Fixed Windows drag'n'drop not showing insert position if the drop
 	  target is inside the same window or process (STR #3209).
 	- Fixed undefined reference building shared cairo library (STR #3276).
diff --git a/src/Fl_Window.cxx b/src/Fl_Window.cxx
index dcab9dd62..ffc7f9f87 100644
--- a/src/Fl_Window.cxx
+++ b/src/Fl_Window.cxx
@@ -53,12 +53,21 @@ void Fl_Window::_Fl_Window() {
   size_range_set = 0;
   minw = maxw = minh = maxh = 0;
   shape_data_ = NULL;
+
 #if FLTK_ABI_VERSION >= 10301
   no_fullscreen_x = 0;
   no_fullscreen_y = 0;
   no_fullscreen_w = w();
   no_fullscreen_h = h();
 #endif
+
+#if FLTK_ABI_VERSION >= 10303
+  fullscreen_screen_top = -1;
+  fullscreen_screen_bottom = -1;
+  fullscreen_screen_left = -1;
+  fullscreen_screen_right = -1;
+#endif
+
   callback((Fl_Callback*)default_callback);
 }