diff --git a/lib/dav4rack/resource.rb b/lib/dav4rack/resource.rb
index 58df04e..4f3e57f 100644
--- a/lib/dav4rack/resource.rb
+++ b/lib/dav4rack/resource.rb
@@ -140,22 +140,23 @@ def parent_exists?
     
     # Return the creation time.
     def creation_date
-      NotImplemented
+      raise NotImplemented
     end
 
     # Return the time of last modification.
     def last_modified
-      NotImplemented
+      raise NotImplemented
     end
     
     # Set the time of last modification.
     def last_modified=(time)
-      NotImplemented
+      # Is this correct?
+      raise NotImplemented
     end
 
     # Return an Etag, an unique hash value for this resource.
     def etag
-      NotImplemented
+      raise NotImplemented
     end
 
     # Return the resource type. Generally only used to specify
@@ -166,12 +167,12 @@ def resource_type
 
     # Return the mime type of this resource.
     def content_type
-      NotImplemented
+      raise NotImplemented
     end
 
     # Return the size in bytes for this resource.
     def content_length
-      NotImplemented
+      raise NotImplemented
     end
 
     # HTTP GET request.