diff --git a/src/libraries/turtle/constraints.hpp b/src/libraries/turtle/constraints.hpp
index 2b80060..74a58ed 100644
--- a/src/libraries/turtle/constraints.hpp
+++ b/src/libraries/turtle/constraints.hpp
@@ -44,6 +44,7 @@ namespace mock
     const constraint< detail::N > N;
 
     MOCK_CONSTRAINT(any, true && &actual)
+    MOCK_CONSTRAINT(affirm, !! actual)
     MOCK_CONSTRAINT(negate, ! actual)
     MOCK_CONSTRAINT(evaluate, actual())
 
diff --git a/src/tests/turtle_test/constraints_test.cpp b/src/tests/turtle_test/constraints_test.cpp
index 6d82b95..05af23f 100644
--- a/src/tests/turtle_test/constraints_test.cpp
+++ b/src/tests/turtle_test/constraints_test.cpp
@@ -25,6 +25,7 @@ BOOST_AUTO_TEST_CASE( all_comparison_constraints_can_be_instanciated )
 BOOST_AUTO_TEST_CASE( constraints_can_be_negated_using_the_not_operator )
 {
     ! mock::any;
+    ! mock::affirm;
     ! mock::negate;
     ! mock::evaluate;
     ! mock::equal( 0 );
@@ -231,6 +232,14 @@ BOOST_AUTO_TEST_CASE( retrieve_uses_assignment_operator )
     mock::retrieve( b ).f_( a );
 }
 
+BOOST_AUTO_TEST_CASE( affirm )
+{
+    int* i = 0;
+    int j;
+    BOOST_CHECK( ! mock::affirm.f_( i ) );
+    BOOST_CHECK( mock::affirm.f_( &j ) );
+}
+
 BOOST_AUTO_TEST_CASE( negate )
 {
     int* i = 0;