diff -ur client_generic.orig/DisplayOutput/OpenGL/glx.cpp client_generic/DisplayOutput/OpenGL/glx.cpp
--- client_generic.orig/DisplayOutput/OpenGL/glx.cpp	2018-07-14 23:10:29.000000000 +0200
+++ client_generic/DisplayOutput/OpenGL/glx.cpp	2019-01-20 19:08:12.055142844 +0100
@@ -466,13 +466,15 @@
 {
     m_VSync = !m_VSync;
 
-    if( GLEE_GLX_SGI_swap_control )
-    {
-        if( m_VSync )
-            glXSwapIntervalSGI(1);
-        else
-            glXSwapIntervalSGI(2);
-    }
+    // broken when extension not available
+
+    //if( GLEE_GLX_SGI_swap_control )
+    //{
+        //if( m_VSync )
+            //glXSwapIntervalSGI(1);
+        //else
+            //glXSwapIntervalSGI(2);
+    //}
 }
 
 /*
