diff -uNr gnome-clocks-3.8.1-orig/src/world.vala gnome-clocks-3.8.1-devel/src/world.vala
--- gnome-clocks-3.8.1-orig/src/world.vala	2013-04-15 12:01:31.000000000 +0200
+++ gnome-clocks-3.8.1-devel/src/world.vala	2013-05-04 21:42:35.834902706 +0200
@@ -204,14 +204,17 @@
 
     private void location_changed () {
         GWeather.Location? l = null;
+	 GWeather.Timezone? t = null;
         if (entry.get_text () == "") {
             entry.set_icon_from_gicon (Gtk.EntryIconPosition.SECONDARY, find_icon);
         } else {
             entry.set_icon_from_gicon (Gtk.EntryIconPosition.SECONDARY, clear_icon);
             l = entry.get_location ();
+	     if (l != null)
+	    	t = l.get_timezone ();
         }
 
-        set_response_sensitive(1, l != null);
+        set_response_sensitive(1, l != null && t != null);
     }
 
     public Item? get_location () {

