diff --git a/lib/rubella/input/base.rb b/lib/rubella/input/base.rb
index b756ebe..fc24218 100644
--- a/lib/rubella/input/base.rb
+++ b/lib/rubella/input/base.rb
@@ -21,7 +21,7 @@ module Rubella
       # @return Rubella::Input::Base
       #
       def self.string(value)
-        raise NotImplementedError "Please override 'self.string' in your "+
+        raise NotImplementedError.new "Please override 'self.string' in your "+
           "concrete implementation"
       end
 
@@ -33,7 +33,7 @@ module Rubella
       # @return Rubella:Input::Base
       #
       def self.file(file_name)
-        raise NotImplementedError "Please override 'self.file' in your "+
+        raise NotImplementedError.new "Please override 'self.file' in your "+
           "concrete implementation"
       end
 
diff --git a/lib/rubella/output/base.rb b/lib/rubella/output/base.rb
index 6c8c876..a6368ee 100644
--- a/lib/rubella/output/base.rb
+++ b/lib/rubella/output/base.rb
@@ -28,8 +28,8 @@ module Rubella
       # @return rendered data
       #
       def render
-        raise NotImplementedError "Please override 'render' in your concrete "+
-          "implementation"
+        raise NotImplementedError.new "Please override 'render' in your "+
+          "concrete implementation"
       end
     end
 
diff --git a/lib/rubella/weighting/base.rb b/lib/rubella/weighting/base.rb
index afdf847..6bfa731 100644
--- a/lib/rubella/weighting/base.rb
+++ b/lib/rubella/weighting/base.rb
@@ -47,8 +47,8 @@ module Rubella
       # @return Rubella::Storage
       #
       def parse input
-        raise NotImplementedError "Please override 'parse' in your concrete "+
-          "implementation"
+        raise NotImplementedError.new "Please override 'parse' in your "+
+          "concrete implementation"
       end
 
     end