--- /dev/null
+--- VirtualBox-6.1.6/src/VBox/Additions/x11/VBoxClient/display-svga-x11.cpp.orig 2020-04-09 19:34:49.000000000 +0200
++++ VirtualBox-6.1.6/src/VBox/Additions/x11/VBoxClient/display-svga-x11.cpp 2020-04-17 00:05:01.199999966 +0200
+@@ -293,7 +293,7 @@
+ }
+ }
+
+-int x11MonitorThreadFunction(RTTHREAD hThreadSelf, void *pvUser)
++DECLCALLBACK(int) x11MonitorThreadFunction(RTTHREAD hThreadSelf, void *pvUser)
+ {
+ (void)hThreadSelf;
+ (void*)pvUser;