diff --git a/sinatra-contrib/lib/sinatra/namespace.rb b/sinatra-contrib/lib/sinatra/namespace.rb
index b7616bc2..63bf1d16 100644
--- a/sinatra-contrib/lib/sinatra/namespace.rb
+++ b/sinatra-contrib/lib/sinatra/namespace.rb
@@ -201,9 +201,10 @@ module Sinatra
       end
 
       def error(*codes, &block)
-        args  = Sinatra::Base.send(:compile!, "ERROR", @pattern, block)
+        args  = Sinatra::Base.send(:compile!, "ERROR", /.*/, block)
         codes = codes.map { |c| Array(c) }.flatten
         codes << Exception if codes.empty?
+        codes << Sinatra::NotFound if codes.include?(404)
 
         codes.each do |c|
           errors = @errors[c] ||= []
@@ -264,7 +265,7 @@ module Sinatra
       end
 
       def prefixed_path(a, b)
-        return a || b || // unless a and b
+        return a || b || /.*/ unless a and b
 
         Mustermann.new(a.to_s + b.to_s)
       rescue
diff --git a/sinatra-contrib/spec/namespace_spec.rb b/sinatra-contrib/spec/namespace_spec.rb
index b4f6e962..8571190e 100644
--- a/sinatra-contrib/spec/namespace_spec.rb
+++ b/sinatra-contrib/spec/namespace_spec.rb
@@ -159,8 +159,6 @@ describe Sinatra::Namespace do
       describe 'conditions' do
         context 'when the namespace has no prefix' do
           specify 'are accepted in the namespace' do
-            skip "Sinatra::Namespace accepts namespace without prefix in conditions"
-
             mock_app do
               namespace(:host_name => 'example.com') { send(verb) { 'yes' }}
               send(verb, '/') { 'no' }
@@ -488,8 +486,6 @@ describe Sinatra::Namespace do
 
       describe 'error handling' do
         it 'can be customized using the not_found block' do
-          skip "Sinatra::Namespace allows not_found blocks"
-
           namespace('/de') do
             not_found { 'nicht gefunden' }
           end
@@ -502,8 +498,6 @@ describe Sinatra::Namespace do
         end
 
         it 'can be customized for specific error codes' do
-          skip "Sinatra::Namespace allows custom error handling"
-
           namespace('/de') do
             error(404) { 'nicht gefunden' }
           end
@@ -516,8 +510,6 @@ describe Sinatra::Namespace do
         end
 
         it 'falls back to the handler defined in the base app' do
-          skip "Sinatra::Namespace allows custom error handling"
-
           mock_app do
             error(404) { 'not found...' }
             namespace('/en') do
@@ -535,8 +527,6 @@ describe Sinatra::Namespace do
         end
 
         it 'can be customized for specific Exception classes' do
-          skip "Sinatra::Namespace allows custom error handling"
-
           mock_app do
             class AError < StandardError; end
             class BError < AError; end