diff --git a/spec/spectator/dsl/mocks/null_double_spec.cr b/spec/spectator/dsl/mocks/null_double_spec.cr
new file mode 100644
index 0000000..5b0e1de
--- /dev/null
+++ b/spec/spectator/dsl/mocks/null_double_spec.cr
@@ -0,0 +1,143 @@
+require "../../../spec_helper"
+
+Spectator.describe "Null double DSL" do
+  private macro expect_null_double(double, actual)
+    %actual_box = Box.box({{actual}})
+    %double_box = Box.box({{double}})
+    expect(%actual_box).to eq(%double_box), {{actual.stringify}} + " is not " + {{double.stringify}}
+  end
+
+  context "specifying methods as keyword args" do
+    double(:test, foo: "foobar", bar: 42)
+    subject(dbl) { double(:test).as_null_object }
+
+    it "defines a double with methods" do
+      aggregate_failures do
+        expect(dbl.foo).to eq("foobar")
+        expect(dbl.bar).to eq(42)
+      end
+    end
+
+    it "compiles types without unions" do
+      aggregate_failures do
+        expect(dbl.foo).to compile_as(String)
+        expect(dbl.bar).to compile_as(Int32)
+      end
+    end
+
+    it "returns self for unexpected messages" do
+      expect_null_double(dbl.baz, dbl)
+    end
+  end
+
+  context "block with stubs" do
+    context "one method" do
+      double(:test2) do
+        stub def foo
+          "one method"
+        end
+      end
+
+      subject(dbl) { double(:test2).as_null_object }
+
+      it "defines a double with methods" do
+        expect(dbl.foo).to eq("one method")
+      end
+
+      it "compiles types without unions" do
+        expect(dbl.foo).to compile_as(String)
+      end
+    end
+
+    context "two methods" do
+      double(:test3) do
+        stub def foo
+          "two methods"
+        end
+
+        stub def bar
+          42
+        end
+      end
+
+      subject(dbl) { double(:test3).as_null_object }
+
+      it "defines a double with methods" do
+        aggregate_failures do
+          expect(dbl.foo).to eq("two methods")
+          expect(dbl.bar).to eq(42)
+        end
+      end
+
+      it "compiles types without unions" do
+        aggregate_failures do
+          expect(dbl.foo).to compile_as(String)
+          expect(dbl.bar).to compile_as(Int32)
+        end
+      end
+    end
+
+    context "empty block" do
+      double(:test4) do
+      end
+
+      subject(dbl) { double(:test4).as_null_object }
+
+      it "defines a double" do
+        expect(dbl).to be_a(Spectator::Double)
+      end
+    end
+
+    context "stub-less method" do
+      double(:test5) do
+        def foo
+          "no stub"
+        end
+      end
+
+      subject(dbl) { double(:test5).as_null_object }
+
+      it "defines a double with methods" do
+        expect(dbl.foo).to eq("no stub")
+      end
+    end
+
+    context "mixing keyword arguments" do
+      double(:test6, foo: "kwargs", bar: 42) do
+        stub def foo
+          "block"
+        end
+
+        stub def baz
+          "block"
+        end
+
+        stub def baz(value)
+          "block2"
+        end
+      end
+
+      subject(dbl) { double(:test6).as_null_object }
+
+      it "overrides the keyword arguments with the block methods" do
+        expect(dbl.foo).to eq("block")
+      end
+
+      it "falls back to the keyword argument value for mismatched arguments" do
+        expect(dbl.foo(42)).to eq("kwargs")
+      end
+
+      it "can call methods defined only by keyword arguments" do
+        expect(dbl.bar).to eq(42)
+      end
+
+      it "can call methods defined only by the block" do
+        expect(dbl.baz).to eq("block")
+      end
+
+      it "can call methods defined by the block with different signatures" do
+        expect(dbl.baz(42)).to eq("block2")
+      end
+    end
+  end
+end
diff --git a/src/spectator/dsl/mocks.cr b/src/spectator/dsl/mocks.cr
index a0e1c71..b879550 100644
--- a/src/spectator/dsl/mocks.cr
+++ b/src/spectator/dsl/mocks.cr
@@ -11,14 +11,23 @@ module Spectator::DSL
     private macro def_double(name, **value_methods, &block)
     {% # Construct a unique type name for the double by using the number of defined doubles.
  index = ::Spectator::DSL::Mocks::DOUBLES.size
- double_type_name = "Double#{index}".id.symbolize
+ double_type_name = "Double#{index}".id
+ null_double_type_name = "NullDouble#{index}".id
 
  # Store information about how the double is defined and its context.
  # This is important for constructing an instance of the double later.
- ::Spectator::DSL::Mocks::DOUBLES << {name.id.symbolize, @type.name(generic_args: false).symbolize, double_type_name} %}
-   
+ ::Spectator::DSL::Mocks::DOUBLES << {name.id.symbolize, @type.name(generic_args: false).symbolize, double_type_name.symbolize} %}
+
+      ::Spectator::Double.define({{double_type_name}}, {{name}}, {{**value_methods}}) do
+        def as_null_object
+          {{null_double_type_name}}.new(@stubs)
+        end
+
+        {% if block %}{{block.body}}{% end %}
+      end
+
       {% begin %}
-        ::Spectator::Double.define({{double_type_name}}, {{name}}, {{**value_methods}}){% if block %} do
+        ::Spectator::NullDouble.define({{null_double_type_name}}, {{name}}, {{**value_methods}}){% if block %} do
           {{block.body}}
         end{% end %}
       {% end %}