diff --git a/include/date/tz.h b/include/date/tz.h
index 1591f80..db39880 100644
--- a/include/date/tz.h
+++ b/include/date/tz.h
@@ -2259,14 +2259,14 @@ struct clock_time_conversion<Clock, Clock>
 namespace ctc_detail
 {
   //Check if TimePoint is time for given clock, 
-  //if so exposes it as type typedef
+  //if not emits hard errorf
   template<typename Clock, typename TimePoint>
   struct return_clock_time
-    : std::enable_if<
-        std::is_same<Clock, typename TimePoint::clock>::value,
-        TimePoint
-      >
-  {};
+  {
+    using clock_time_point = std::chrono::time_point<Clock, typename TimePoint::duration>;
+    static_assert(std::is_same<TimePoint, clock_time_point>::value, "time point with appropariate clock shall be returned");
+    using type = TimePoint;
+  };
 
   // Check if Clock has to_sys method accepting TimePoint with given duration const& and returning sys_time
   // If so has nested type member equal to return type to_sys.
@@ -2276,7 +2276,7 @@ namespace ctc_detail
 
   template<typename Clock, typename Duration>
   struct return_to_sys<Clock, Duration, decltype(Clock::to_sys(std::declval<std::chrono::time_point<Clock, Duration> const&>()), void())>
-    : return_clock_time<std::chrono::system_clock, typename std::decay<decltype(Clock::to_sys(std::declval<std::chrono::time_point<Clock, Duration> const&>()))>::type>
+    : return_clock_time<std::chrono::system_clock, decltype(Clock::to_sys(std::declval<std::chrono::time_point<Clock, Duration> const&>()))>
   {};
 
   // Similiar to above
@@ -2286,7 +2286,7 @@ namespace ctc_detail
 
   template<typename Clock, typename Duration>
   struct return_from_sys<Clock, Duration, decltype(Clock::from_sys(std::declval<std::chrono::time_point<std::chrono::system_clock, Duration> const&>()), void())>
-    : return_clock_time<Clock, typename std::decay<decltype(Clock::from_sys(std::declval<std::chrono::time_point<std::chrono::system_clock, Duration> const&>()))>::type>
+    : return_clock_time<Clock, decltype(Clock::from_sys(std::declval<std::chrono::time_point<std::chrono::system_clock, Duration> const&>()))>
   {};
 
   // Similiar to above
@@ -2296,7 +2296,7 @@ namespace ctc_detail
 
   template<typename Clock, typename Duration>
   struct return_to_utc<Clock, Duration, decltype(Clock::to_utc(std::declval<std::chrono::time_point<Clock, Duration> const&>()), void())>
-    : return_clock_time<utc_clock, typename std::decay<decltype(Clock::to_utc(std::declval<std::chrono::time_point<Clock, Duration> const&>()))>::type>
+    : return_clock_time<utc_clock, decltype(Clock::to_utc(std::declval<std::chrono::time_point<Clock, Duration> const&>()))>
   {};
 
   // Similiar to above
@@ -2306,7 +2306,7 @@ namespace ctc_detail
 
   template<typename Clock, typename Duration>
   struct return_from_utc<Clock, Duration, decltype(Clock::from_utc(std::declval<std::chrono::time_point<utc_clock, Duration> const&>()), void())>
-    : return_clock_time<Clock, typename std::decay<decltype(Clock::from_utc(std::declval<std::chrono::time_point<utc_clock, Duration> const&>()))>::type>
+    : return_clock_time<Clock, decltype(Clock::from_utc(std::declval<std::chrono::time_point<utc_clock, Duration> const&>()))>
   {};
 }
 
diff --git a/test/tz_test/to_sys_return_int.fail.cpp b/test/tz_test/to_sys_return_int.fail.cpp
new file mode 100644
index 0000000..76c8551
--- /dev/null
+++ b/test/tz_test/to_sys_return_int.fail.cpp
@@ -0,0 +1,49 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2017 Tomasz Kamiński
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+#include "tz.h"
+
+struct bad_clock 
+{
+  using duration = std::chrono::system_clock::duration;
+  using rep = duration::rep;
+  using period = duration::period;
+  using time_point = std::chrono::time_point<bad_clock, duration>;
+
+  template<typename Duration>
+  static
+  int 
+  to_sys(std::chrono::time_point<bad_clock, Duration> const& tp)
+  {
+    return tp.time_since_epoch().count();
+  }
+};
+
+int
+main()
+{
+    using namespace date;
+    using sys_clock = std::chrono::system_clock;
+
+    auto bt = bad_clock::time_point();
+    clock_cast<sys_clock>(bt);
+}
diff --git a/test/tz_test/to_sys_return_reference.cpp b/test/tz_test/to_sys_return_reference.cpp
new file mode 100644
index 0000000..1f8527f
--- /dev/null
+++ b/test/tz_test/to_sys_return_reference.cpp
@@ -0,0 +1,51 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2017 Tomasz Kamiński
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+#include "tz.h"
+
+struct bad_clock 
+{
+  using duration = std::chrono::system_clock::duration;
+  using rep = duration::rep;
+  using period = duration::period;
+  using time_point = std::chrono::time_point<bad_clock, duration>;
+
+  template<typename Duration>
+  static
+  date::sys_time<Duration> const&
+  to_sys(std::chrono::time_point<bad_clock, Duration> const& tp)
+  {
+    static date::sys_time<Duration> val;
+    val = date::sys_time<Duration>(tp.time_since_epoch());
+    return val;
+  }
+};
+
+int
+main()
+{
+    using namespace date;
+    using sys_clock = std::chrono::system_clock;
+
+    auto bt = bad_clock::time_point();
+    clock_cast<sys_clock>(bt);
+}
diff --git a/test/tz_test/to_sys_return_utc_time.fail.cpp b/test/tz_test/to_sys_return_utc_time.fail.cpp
new file mode 100644
index 0000000..352b983
--- /dev/null
+++ b/test/tz_test/to_sys_return_utc_time.fail.cpp
@@ -0,0 +1,49 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2017 Tomasz Kamiński
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+#include "tz.h"
+
+struct bad_clock 
+{
+  using duration = std::chrono::system_clock::duration;
+  using rep = duration::rep;
+  using period = duration::period;
+  using time_point = std::chrono::time_point<bad_clock, duration>;
+
+  template<typename Duration>
+  static
+  date::utc_time<Duration> 
+  to_sys(std::chrono::time_point<bad_clock, Duration> const& tp)
+  {
+    return utc_time<Duration>(tp.time_since_epoch());
+  }
+};
+
+int
+main()
+{
+    using namespace date;
+    using sys_clock = std::chrono::system_clock;
+
+    auto bt = bad_clock::time_point();
+    clock_cast<sys_clock>(bt);
+}