--- vcl/inc/unx/saltype.h	2019-12-05 20:59:23.000000000 +0100
+++ vcl/inc/unx/saltype.h	2020-03-17 18:23:05.585171000 +0100
@@ -18,8 +18,8 @@
 public:
     explicit SalX11Screen(unsigned int nXScreen) : mnXScreen( nXScreen ) {}
     unsigned int getXScreen() const { return mnXScreen; }
-    bool operator==(const SalX11Screen &rOther) { return rOther.mnXScreen == mnXScreen; }
-    bool operator!=(const SalX11Screen &rOther) { return rOther.mnXScreen != mnXScreen; }
+    bool operator==(const SalX11Screen &rOther) const { return rOther.mnXScreen == mnXScreen; }
+    bool operator!=(const SalX11Screen &rOther) const { return rOther.mnXScreen != mnXScreen; }
 };
 
 #endif // INCLUDED_VCL_INC_UNX_SALTYPE_H