diff --git a/lcl/interfaces/gtk/gtkwidgetset.inc b/lcl/interfaces/gtk/gtkwidgetset.inc
index e959706062..79e9e2c677 100644
--- a/lcl/interfaces/gtk/gtkwidgetset.inc
+++ b/lcl/interfaces/gtk/gtkwidgetset.inc
@@ -540,6 +540,7 @@ var
   thrash: char;
 begin
   // wake up GUI thread by sending a byte through the threadsync pipe
+  thrash:='l';
   fpwrite(threadsync_pipeout, thrash, 1);
 end;