diff --git a/build/vc80/errors_test.vcproj b/build/vc80/errors_test.vcproj
index b273c26..4d8a3d6 100644
--- a/build/vc80/errors_test.vcproj
+++ b/build/vc80/errors_test.vcproj
@@ -206,10 +206,6 @@
 				RelativePath="..\..\src\tests\errors_test\constraint_value_of_wrong_type_in_builtin_constraint.cpp"
 				>
 			</File>
-			<File
-				RelativePath="..\..\src\tests\errors_test\custom_constraint_call_operator_not_const.cpp"
-				>
-			</File>
 			<File
 				RelativePath="..\..\src\tests\errors_test\mismatch_type_in_returns_int_action.cpp"
 				>
diff --git a/src/libraries/turtle/check.hpp b/src/libraries/turtle/check.hpp
index fb35cd6..12a336f 100644
--- a/src/libraries/turtle/check.hpp
+++ b/src/libraries/turtle/check.hpp
@@ -64,7 +64,7 @@ namespace detail
     public:
         virtual ~check_base() {}
 
-        virtual bool operator()( Actual ) const = 0;
+        virtual bool operator()( Actual ) = 0;
 
         friend std::ostream& operator<<( std::ostream& s, const check_base& c )
         {
@@ -88,7 +88,7 @@ namespace detail
                 Actual > ));
         }
     private:
-        virtual bool operator()( Actual actual ) const
+        virtual bool operator()( Actual actual )
         {
             return actual == boost::unwrap_ref( expected_ );
         }
@@ -111,7 +111,7 @@ namespace detail
             BOOST_CONCEPT_ASSERT(( FunctorCompatible< Constraint, Actual > ));
         }
     private:
-        virtual bool operator()( Actual actual ) const
+        virtual bool operator()( Actual actual )
         {
             return c_( actual );
         }
@@ -137,7 +137,7 @@ namespace detail
             BOOST_CONCEPT_ASSERT(( FunctorCompatible< Functor, Actual > ));
         }
     private:
-        virtual bool operator()( Actual actual ) const
+        virtual bool operator()( Actual actual )
         {
             return f_( actual );
         }
diff --git a/src/tests/errors_test/custom_constraint_call_operator_not_const.cpp b/src/tests/errors_test/custom_constraint_call_operator_not_const.cpp
deleted file mode 100644
index add1ca4..0000000
--- a/src/tests/errors_test/custom_constraint_call_operator_not_const.cpp
+++ /dev/null
@@ -1,27 +0,0 @@
-//
-//  Copyright Mathieu Champlon 2011
-//
-//  Distributed under the Boost Software License, Version 1.0. (See
-//  accompanying file LICENSE_1_0.txt or copy at
-//  http://www.boost.org/LICENSE_1_0.txt)
-//
-
-#include <turtle/mock.hpp>
-
-namespace
-{
-    MOCK_CLASS( my_class )
-    {
-        MOCK_METHOD_EXT( my_method, 1, void( int ), my_method )
-    };
-    struct custom_constraint
-    {
-        template< typename Actual >
-        bool operator()( Actual actual );
-    };
-    void test_case()
-    {
-        my_class c;
-        MOCK_EXPECT( c, my_method ).with( mock::constraint< custom_constraint >( custom_constraint() ) );
-    }
-}
diff --git a/src/tests/turtle_test/integration_test.cpp b/src/tests/turtle_test/integration_test.cpp
index f226401..7183008 100644
--- a/src/tests/turtle_test/integration_test.cpp
+++ b/src/tests/turtle_test/integration_test.cpp
@@ -413,6 +413,25 @@ BOOST_AUTO_TEST_CASE( using_custom_constraint )
     BOOST_CHECK_EQUAL( expected, s.str() );
 }
 
+namespace
+{
+    struct custom_constraint_with_non_const_operator
+    {
+        template< typename Actual >
+        bool operator()( Actual actual )
+        {
+            return actual == 42;
+        }
+    };
+}
+
+BOOST_AUTO_TEST_CASE( custom_constraint_function_operator_does_not_need_to_be_const )
+{
+    MOCK_FUNCTOR( void( float ) ) f;
+    MOCK_EXPECT( f, _ ).with( mock::constraint< custom_constraint_with_non_const_operator >( custom_constraint_with_non_const_operator() ) );
+    f( 42 );
+}
+
 BOOST_AUTO_TEST_CASE( boost_reference_wrapper_is_supported_in_value_constraint )
 {
     MOCK_FUNCTOR( void( const std::string& ) ) f;