diff --git a/build/vc80/turtle.vcproj b/build/vc80/turtle.vcproj
index a311d55..2db2e54 100644
--- a/build/vc80/turtle.vcproj
+++ b/build/vc80/turtle.vcproj
@@ -196,10 +196,6 @@
 				RelativePath="..\..\src\libraries\turtle\invocation.hpp"
 				>
 			</File>
-			<File
-				RelativePath="..\..\src\libraries\turtle\is_comparable.hpp"
-				>
-			</File>
 			<File
 				RelativePath="..\..\src\libraries\turtle\is_formattable.hpp"
 				>
diff --git a/build/vc80/turtle_test.vcproj b/build/vc80/turtle_test.vcproj
index 8c02089..a429b86 100644
--- a/build/vc80/turtle_test.vcproj
+++ b/build/vc80/turtle_test.vcproj
@@ -214,10 +214,6 @@
 				RelativePath="..\..\src\tests\turtle_test\invocation_test.cpp"
 				>
 			</File>
-			<File
-				RelativePath="..\..\src\tests\turtle_test\is_comparable_test.cpp"
-				>
-			</File>
 			<File
 				RelativePath="..\..\src\tests\turtle_test\is_formattable_test.cpp"
 				>
diff --git a/src/libraries/turtle/check.hpp b/src/libraries/turtle/check.hpp
index 90ce0ca..6315330 100644
--- a/src/libraries/turtle/check.hpp
+++ b/src/libraries/turtle/check.hpp
@@ -10,7 +10,6 @@
 #define MOCK_CHECK_HPP_INCLUDED
 
 #include "is_functor.hpp"
-#include "is_comparable.hpp"
 #include "constraints.hpp"
 #include "operators.hpp"
 #include "format.hpp"
@@ -122,12 +121,7 @@ namespace detail
     template< typename Actual, typename Functor >
     class check< Actual, Functor,
         BOOST_DEDUCED_TYPENAME boost::enable_if<
-            boost::mpl::or_<
-                detail::is_functor< Functor >,
-                boost::mpl::not_<
-                    detail::is_comparable< Actual, Functor >
-                >
-            >
+            detail::is_functor< Functor >
         >::type
     > : public check_base< Actual >
     {
diff --git a/src/tests/turtle_test/integration_test.cpp b/src/tests/turtle_test/integration_test.cpp
index 3291951..f9e75d8 100644
--- a/src/tests/turtle_test/integration_test.cpp
+++ b/src/tests/turtle_test/integration_test.cpp
@@ -335,7 +335,7 @@ namespace
 
     struct custom_argument
     {
-        friend std::ostream& operator<<( std::ostream& s, const custom_argument& )
+        friend std::ostream& operator<<( std::ostream& s, custom_argument )
         {
             serialized = true;
             return s;
@@ -344,11 +344,11 @@ namespace
     struct custom_constraint
     {
         template< typename Actual >
-        bool operator()( Actual ) const
+        friend bool operator==( Actual, custom_constraint )
         {
             return true;
         }
-        friend std::ostream& operator<<( std::ostream& s, const custom_constraint& )
+        friend std::ostream& operator<<( std::ostream& s, custom_constraint )
         {
             serialized = true;
             return s;