diff --git a/actionpack/lib/action_controller/log_subscriber.rb b/actionpack/lib/action_controller/log_subscriber.rb
index 823a1050b566b1145d3325f0f320adca02534d9e..e920a33765c8e99b7cd669c8e6e3a64c1599e4df 100644
--- a/actionpack/lib/action_controller/log_subscriber.rb
+++ b/actionpack/lib/action_controller/log_subscriber.rb
@@ -50,7 +50,7 @@ def send_data(event)
 
     def unpermitted_parameters(event)
       unpermitted_keys = event.payload[:keys]
-      debug("Unpermitted parameters: #{unpermitted_keys.join(", ")}")
+      debug("Unpermitted parameter#{'s' if unpermitted_keys.size > 1}: #{unpermitted_keys.join(", ")}")
     end
 
     def deep_munge(event)
diff --git a/actionpack/lib/action_controller/metal/strong_parameters.rb b/actionpack/lib/action_controller/metal/strong_parameters.rb
index 48a916f2b18fb65d9899b518196098368d4b4579..aff083b5025b70927c75d7e3dfc88a3b13c642d7 100644
--- a/actionpack/lib/action_controller/metal/strong_parameters.rb
+++ b/actionpack/lib/action_controller/metal/strong_parameters.rb
@@ -32,7 +32,7 @@ class UnpermittedParameters < IndexError
 
     def initialize(params) # :nodoc:
       @params = params
-      super("found unpermitted parameters: #{params.join(", ")}")
+      super("found unpermitted parameter#{'s' if params.size > 1 }: #{params.join(", ")}")
     end
   end
 
diff --git a/actionpack/test/controller/parameters/log_on_unpermitted_params_test.rb b/actionpack/test/controller/parameters/log_on_unpermitted_params_test.rb
index 22e603b8815032b83615621d3e6b18923fb4d8f0..9ce04b9aebe478703a662868ec7fd468b6417fe3 100644
--- a/actionpack/test/controller/parameters/log_on_unpermitted_params_test.rb
+++ b/actionpack/test/controller/parameters/log_on_unpermitted_params_test.rb
@@ -10,23 +10,45 @@ def teardown
     ActionController::Parameters.action_on_unpermitted_parameters = false
   end
 
-  test "logs on unexpected params" do
+  test "logs on unexpected param" do
     params = ActionController::Parameters.new({
       book: { pages: 65 },
       fishing: "Turnips"
     })
 
-    assert_logged("Unpermitted parameters: fishing") do
+    assert_logged("Unpermitted parameter: fishing") do
       params.permit(book: [:pages])
     end
   end
 
-  test "logs on unexpected nested params" do
+  test "logs on unexpected params" do
+    params = ActionController::Parameters.new({
+      book: { pages: 65 },
+      fishing: "Turnips",
+      car: "Mersedes"
+    })
+
+    assert_logged("Unpermitted parameters: fishing, car") do
+      params.permit(book: [:pages])
+    end
+  end
+
+  test "logs on unexpected nested param" do
     params = ActionController::Parameters.new({
       book: { pages: 65, title: "Green Cats and where to find then." }
     })
 
-    assert_logged("Unpermitted parameters: title") do
+    assert_logged("Unpermitted parameter: title") do
+      params.permit(book: [:pages])
+    end
+  end
+
+  test "logs on unexpected nested params" do
+    params = ActionController::Parameters.new({
+      book: { pages: 65, title: "Green Cats and where to find then.", author: "G. A. Dog" }
+    })
+
+    assert_logged("Unpermitted parameters: title, author") do
       params.permit(book: [:pages])
     end
   end