diff --git a/CHANGELOG.md b/CHANGELOG.md
index 3c17f18d3..9b0f2660a 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -20,6 +20,7 @@
 * [#1249](https://github.com/ruby-grape/grape/pull/1249): Don't fail even if invalid type value is passed to default validator - [@namusyaka](https://github.com/namusyaka).
 * [#1263](https://github.com/ruby-grape/grape/pull/1263): Fix `route :any, '*path'` breaking generated `OPTIONS`, Method Not Allowed routes - [@arempe93](https://github.com/arempe93).
 * [#1266](https://github.com/ruby-grape/grape/pull/1266): Fix `Allow` header including `OPTIONS` when `do_not_route_options!` is active - [@arempe93](https://github.com/arempe93).
+* [#1264](https://github.com/ruby-grape/grape/pull/1264): Unify behavior of default_error_status - [@namusyaka](https://github.com/namusyaka).
 
 0.14.0 (12/07/2015)
 ===================
diff --git a/README.md b/README.md
index ec11d2699..125606135 100644
--- a/README.md
+++ b/README.md
@@ -1612,6 +1612,8 @@ class API < Grape::API
 end
 ```
 
+Of course, `default_error_status` does not depend on the timing of route definition, so mounted application can also use the default error status code.
+
 ### Handling 404
 
 For Grape to handle all the 404s for your API, it can be useful to use a catch-all.
diff --git a/UPGRADING.md b/UPGRADING.md
index 0f4b32aa3..ccba4bb0c 100644
--- a/UPGRADING.md
+++ b/UPGRADING.md
@@ -1,6 +1,39 @@
 Upgrading Grape
 ===============
 
+#### Changes to  behavior of `default_error_status`
+
+The `default_error_status` method had been depending on the timing of route definition.
+
+Currently, the difference of behaviors has been unified. The following code is treated as same meaning.
+
+```ruby
+class A < Grape::API
+  default_error_status 400
+end
+
+class API < Grape::API
+  mount A
+end
+
+A.get '/error' do
+  error!('error')
+end
+```
+
+```ruby
+class B < Grape::API
+  default_error_status 400
+  get '/error' do
+    error!('error')
+  end
+end
+
+class API < Grape::API
+  mount B
+end
+```
+
 ### Upgrading to >= 0.15.0
 
 #### Changes to availability of `:with` option of `rescue_from` method
diff --git a/lib/grape/dsl/routing.rb b/lib/grape/dsl/routing.rb
index 699649c4d..a0d6313a5 100644
--- a/lib/grape/dsl/routing.rb
+++ b/lib/grape/dsl/routing.rb
@@ -87,6 +87,11 @@ def mount(mounts)
               change!
             end
 
+            app.endpoints.each do |endpoint|
+              current_error_status = namespace_inheritable(:default_error_status) || 500
+              endpoint.namespace_inheritable(:default_error_status, current_error_status)
+            end if !app.is_a?(Proc) && app.ancestors.include?(Grape::API)
+
             endpoints << Grape::Endpoint.new(
               in_setting,
               method: :any,
diff --git a/spec/grape/api_spec.rb b/spec/grape/api_spec.rb
index 90349ca89..1b3b56592 100644
--- a/spec/grape/api_spec.rb
+++ b/spec/grape/api_spec.rb
@@ -1983,6 +1983,37 @@ def self.call(object, _env)
       get '/exception'
       expect(last_response.status).to eql 400
     end
+
+    context 'with mounted api' do
+      before do
+        subject.version 'v1', using: :path
+        subject.default_error_status 400
+      end
+
+      it 'inherits default error status' do
+        api = Class.new(Grape::API)
+        subject.mount api
+        api.get('/error') do
+          error!('error!')
+        end
+
+        get '/v1/error'
+        expect(last_response.status).to eql 400
+        expect(last_response.body).to eq('error!')
+      end
+
+      it 'inherits default error status even if target route is registered before mounting self' do
+        api = Class.new(Grape::API)
+        api.get('/error') do
+          error!('error!')
+        end
+        subject.mount api
+
+        get '/v1/error'
+        expect(last_response.status).to eql 400
+        expect(last_response.body).to eq('error!')
+      end
+    end
   end
 
   context 'http_codes' do