diff --git a/Changelog.md b/Changelog.md
index 5167e1d76..7a9cafb20 100644
--- a/Changelog.md
+++ b/Changelog.md
@@ -55,6 +55,7 @@ bind to an UNIX socket at `unix:tmp/diaspora.sock`. Please change your local
 * Precompile facebox images [#6105](https://github.com/diaspora/diaspora/pull/6105)
 * Fix wrong closing a-tag [#6111](https://github.com/diaspora/diaspora/pull/6111)
 * Fix mobile more-button wording when there are less than 15 posts [#6118](https://github.com/diaspora/diaspora/pull/6118)
+* Fix reappearing flash boxes during sign-in [#6146](https://github.com/diaspora/diaspora/pull/6146)
 
 ## Features
 * Add configuration options for some debug logs [#6090](https://github.com/diaspora/diaspora/pull/6090)
diff --git a/app/controllers/registrations_controller.rb b/app/controllers/registrations_controller.rb
index 611b1cf94..4697592fb 100644
--- a/app/controllers/registrations_controller.rb
+++ b/app/controllers/registrations_controller.rb
@@ -20,7 +20,7 @@ class RegistrationsController < Devise::RegistrationsController
     else
       @user.errors.delete(:person)
 
-      flash[:error] = @user.errors.full_messages.join(" - ")
+      flash.now[:error] = @user.errors.full_messages.join(" - ")
       logger.info "event=registration status=failure errors='#{@user.errors.full_messages.join(', ')}'"
       render :action => 'new', :layout => 'with_header'
     end
diff --git a/features/desktop/signs_up.feature b/features/desktop/signs_up.feature
index 46ee98c3f..0f955a19c 100644
--- a/features/desktop/signs_up.feature
+++ b/features/desktop/signs_up.feature
@@ -88,3 +88,12 @@ Feature: new user registration
     And I press "Sign up"
     Then I should not be able to sign up
     And I should have a validation error on "user_password, user_password_confirmation"
+
+  Scenario: User signs up with an already existing username and email and then tries to sign in (Issue #6136)
+    When I log out manually
+    And I go to the new user registration page
+    And I fill in the new user form with an existing email and username
+    And I submit the form
+    Then I should see a flash message indicating failure
+    When I click the sign in button
+    Then I should not see a flash message indicating failure
diff --git a/features/step_definitions/custom_web_steps.rb b/features/step_definitions/custom_web_steps.rb
index 03fd058d7..30fff7cc9 100644
--- a/features/step_definitions/custom_web_steps.rb
+++ b/features/step_definitions/custom_web_steps.rb
@@ -252,6 +252,10 @@ Then /^I should see a flash message indicating failure$/ do
   flash_message_failure?.should be true
 end
 
+Then /^I should not see a flash message indicating failure$/ do
+  expect { flash_message_failure?.should }.to raise_error(Capybara::ElementNotFound)
+end
+
 Then /^I should see a flash message with a warning$/ do
   flash_message_alert?.should be true
 end
diff --git a/features/step_definitions/user_steps.rb b/features/step_definitions/user_steps.rb
index 5c9c55164..b23e37597 100644
--- a/features/step_definitions/user_steps.rb
+++ b/features/step_definitions/user_steps.rb
@@ -206,7 +206,7 @@ Given /^I visit alice's invitation code url$/ do
   visit invite_code_path(invite_code)
 end
 
-When /^I fill in the new user form$/ do
+When /^I fill in the new user form/ do
   fill_in_new_user_form
 end
 
@@ -215,3 +215,7 @@ And /^I should be able to friend Alice$/ do
   step 'I should see "Add contact"'
   step "I should see \"#{alice.name}\""
 end
+
+When /^I click the sign in button$/ do
+  click_link "Sign in"
+end