-# Check for the presence of the "VidMode" X Window System extension.
-# Defines "VIDMODE" and sets the $(VIDMODE) variable to "yes" if the extension
-# is present.
-AC_DEFUN([X11_EXT_VIDMODE],
+# Check for the presence of the "Sync" X Window System extension.
+# Defines "SYNC", sets the $(SYNC) variable to "yes", and sets the $(LIBS)
+# appropriately if the extension is present.
+AC_DEFUN([X11_EXT_SYNC],