diff --git a/lib/excon.rb b/lib/excon.rb
index 2a9eee03..ded48dcf 100644
--- a/lib/excon.rb
+++ b/lib/excon.rb
@@ -63,7 +63,7 @@ def display_warning(warning)
       end
 
       if @raise_on_warnings
-        raise warning
+        raise Error::Warning.new(warning)
       end
     end
 
diff --git a/lib/excon/error.rb b/lib/excon/error.rb
index a31094f0..04bd4a36 100644
--- a/lib/excon/error.rb
+++ b/lib/excon/error.rb
@@ -6,6 +6,7 @@ class Error < StandardError
 
     class StubNotFound < Error; end
     class InvalidStub < Error; end
+    class Warning < Error; end
 
     # Socket related errors
     class Socket < Error
diff --git a/spec/requests/unix_socket_spec.rb b/spec/requests/unix_socket_spec.rb
index dd548834..6ec735c2 100644
--- a/spec/requests/unix_socket_spec.rb
+++ b/spec/requests/unix_socket_spec.rb
@@ -1,25 +1,17 @@
 require "spec_helper"
 
 describe Excon::Connection do
+  include_context('stubs')
   context "when speaking to a UNIX socket" do
     context "Host header handling" do
       before do
-        responder = ->(req) do
+        Excon.stub do |req|
           {
             body: req[:headers].to_json,
             status: 200,
           }
         end
-
-        @original_mock = Excon.defaults[:mock]
-        Excon.defaults[:mock] = true
-        Excon.stub({}, responder)
-      end
-
-      after do
-        Excon.defaults[:mock] = @original_mock
       end
-
       it "sends an empty Host= by default" do
         conn = Excon::Connection.new(
           scheme: "unix",
diff --git a/spec/requests/validation_spec.rb b/spec/requests/validation_spec.rb
new file mode 100644
index 00000000..f3e3d0f5
--- /dev/null
+++ b/spec/requests/validation_spec.rb
@@ -0,0 +1,80 @@
+describe Excon::Connection do
+  include_context('stubs')
+  describe 'validating parameters' do
+    class FooMiddleware < Excon::Middleware::Base
+      def self.valid_parameter_keys
+        [:foo]
+      end
+    end
+
+    let(:foo_stack) do
+      Excon.defaults[:middlewares] + [FooMiddleware]
+    end
+
+    def expect_parameter_warning(validation, key)
+      expect { yield }.to raise_error(Excon::Error::Warning, "Invalid Excon #{validation} keys: #{key.inspect}")
+    end
+
+    context 'with default middleware' do
+      it 'Connection.new warns on invalid parameter keys' do
+        expect_parameter_warning('connection', :foo) do
+          Excon.new('http://foo', :foo => :bar)
+        end
+      end
+
+      it 'Connection#request warns on invalid parameter keys' do
+        conn = Excon.new('http://foo')
+        expect_parameter_warning('request', :foo) do
+          conn.request(:foo => :bar)
+        end
+      end
+    end
+
+    context 'with custom middleware at instantiation' do
+      it 'Connection.new accepts parameters that are valid for the provided middleware' do
+        Excon.new('http://foo', :foo => :bar, :middlewares => foo_stack)
+      end
+
+      it 'Connection.new warns on parameters that are not valid for the provided middleware' do
+        expect_parameter_warning('connection', :bar) do
+          Excon.new('http://foo', :bar => :baz, :middlewares => foo_stack)
+        end
+      end
+
+      it 'Connection#request accepts parameters that are valid for the provided middleware' do
+        Excon.stub({}, {})
+        conn = Excon.new('http://foo', :middlewares => foo_stack)
+        conn.request(:foo => :bar)
+      end
+
+      it 'Connection#request warns on parameters that are not valid for the provided middleware' do
+        conn = Excon.new('http://foo', :middlewares => foo_stack)
+        expect_parameter_warning('request', :bar) do
+          conn.request(:bar => :baz)
+        end
+      end
+    end
+
+    context 'with custom middleware at request time' do
+      it 'Connection#request accepts parameters that are valid for the provided middleware' do
+        Excon.stub({}, {})
+        conn = Excon.new('http://foo')
+        conn.request(:foo => :bar, :middlewares => foo_stack)
+      end
+
+      it 'Connection#request warns on parameters that are not valid for the request middleware' do
+        conn = Excon.new('http://foo')
+        expect_parameter_warning('request', :bar) do
+          conn.request(:bar => :baz, :middlewares => foo_stack)
+        end
+      end
+
+      it 'Connection#request warns on parameters from instantiation that are not valid for the request middleware' do
+        conn = Excon.new('http://foo', :foo => :bar, :middlewares => foo_stack)
+        expect_parameter_warning('connection', :foo) do
+          conn.request(:middlewares => Excon.defaults[:middlewares])
+        end
+      end
+    end
+  end
+end
\ No newline at end of file
diff --git a/spec/support/shared_contexts/test_stub_context.rb b/spec/support/shared_contexts/test_stub_context.rb
new file mode 100644
index 00000000..8c2fafb0
--- /dev/null
+++ b/spec/support/shared_contexts/test_stub_context.rb
@@ -0,0 +1,11 @@
+shared_context "stubs" do 
+  before do
+    @original_mock = Excon.defaults[:mock]
+    Excon.defaults[:mock] = true
+  end
+
+  after do
+    Excon.defaults[:mock] = @original_mock
+    Excon.stubs.clear
+  end
+end
\ No newline at end of file