diff --git a/dwss.c b/dwss.cc
similarity index 96%
rename from dwss.c
rename to dwss.cc
index 5461737..085d5dc 100644
--- a/dwss.c
+++ b/dwss.cc
@@ -143,10 +143,10 @@ main (int   argc,
 
     drawing_area = gtk_drawing_area_new ();
 
-    glconfig = gdk_gl_config_new_by_mode(
-            GDK_GL_MODE_RGB |
-            GDK_GL_MODE_DEPTH |
-            GDK_GL_MODE_DOUBLE);
+    glconfig = gdk_gl_config_new_by_mode( (GdkGLConfigMode)
+            ( GDK_GL_MODE_RGB |
+              GDK_GL_MODE_DEPTH |
+              GDK_GL_MODE_DOUBLE ) );
 
     if (!glconfig)
     {