diff --git a/actionpack/CHANGELOG.md b/actionpack/CHANGELOG.md
index 0e54b33168..0536d39e42 100644
--- a/actionpack/CHANGELOG.md
+++ b/actionpack/CHANGELOG.md
@@ -2,4 +2,8 @@
 
     *Piotr Sarnacki*, *Łukasz Strzałkowski*
 
+*   Fix removing trailing slash for mounted apps #3215
+
+    *Piotr Sarnacki*
+
 Please check [4-0-stable](https://github.com/rails/rails/blob/4-0-stable/actionpack/CHANGELOG.md) for previous changes.
diff --git a/actionpack/lib/action_dispatch/journey/router.rb b/actionpack/lib/action_dispatch/journey/router.rb
index 419e665d12..da32f1bfe7 100644
--- a/actionpack/lib/action_dispatch/journey/router.rb
+++ b/actionpack/lib/action_dispatch/journey/router.rb
@@ -54,7 +54,7 @@ def initialize(routes, options)
       end
 
       def call(env)
-        env['PATH_INFO'] = Utils.normalize_path(env['PATH_INFO'])
+        env['PATH_INFO'] = normalize_path(env['PATH_INFO'])
 
         find_routes(env).each do |match, parameters, route|
           script_name, path_info, set_params = env.values_at('SCRIPT_NAME',
@@ -103,6 +103,12 @@ def visualizer
 
       private
 
+        def normalize_path(path)
+          path = "/#{path}"
+          path.squeeze!('/')
+          path
+        end
+
         def partitioned_routes
           routes.partitioned_routes
         end
diff --git a/actionpack/test/dispatch/mount_test.rb b/actionpack/test/dispatch/mount_test.rb
index e5e28c28be..30e95a0b75 100644
--- a/actionpack/test/dispatch/mount_test.rb
+++ b/actionpack/test/dispatch/mount_test.rb
@@ -33,6 +33,11 @@ def app
     Router
   end
 
+  def test_trailing_slash_is_not_removed_from_path_info
+    get "/sprockets/omg/"
+    assert_equal "/sprockets -- /omg/", response.body
+  end
+
   def test_mounting_sets_script_name
     get "/sprockets/omg"
     assert_equal "/sprockets -- /omg", response.body