diff --git a/gdk/x11/gdkdisplay-x11.c b/gdk/x11/gdkdisplay-x11.c
index 1eb62ffba8..95b22f655a 100644
--- a/gdk/x11/gdkdisplay-x11.c
+++ b/gdk/x11/gdkdisplay-x11.c
@@ -2360,8 +2360,8 @@ _gdk_x11_display_error_event (GdkDisplay  *display,
                          "  (Details: serial %ld error_code %d request_code %d minor_code %d)\n"
                          "  (Note to programmers: normally, X errors are reported asynchronously;\n"
                          "   that is, you will receive the error a while after causing it.\n"
-                         "   To debug your program, run it with the --sync command line\n"
-                         "   option to change this behavior. You can then get a meaningful\n"
+                         "   To debug your program, run it with the GDK_SYNCHRONIZE environment\n"
+                         "   variable to change this behavior. You can then get a meaningful\n"
                          "   backtrace from your debugger if you break on the gdk_x_error() function.)",
                          g_get_prgname (),
                          buf,