diff --git a/lib/geocoder/lookups/base.rb b/lib/geocoder/lookups/base.rb
index 3d8c66febd4c514153b74ad9faf780ea8abfa98a..ae8c8cf54228d44cd56bc7be66cb451c4cd65122 100644
--- a/lib/geocoder/lookups/base.rb
+++ b/lib/geocoder/lookups/base.rb
@@ -75,6 +75,9 @@ module Geocoder
           end
         elsif defined?(ActiveSupport::JSON)
           ActiveSupport::JSON.decode(raw_data)
+        else
+          raise Geocoder::Error, "No JSON-parsing library found. " +
+            "Please install either the 'json' or 'activesupport' gem."
         end
       end