diff --git a/cxx/CMakeLists.txt b/cxx/CMakeLists.txt
index 503fda5..ec49715 100644
--- a/cxx/CMakeLists.txt
+++ b/cxx/CMakeLists.txt
@@ -128,6 +128,7 @@ set(MCC_LIBRARY_SRC mcc_mount.h mcc_mount_coord.h mcc_mount_events_states.h mcc_
 set(MCC_LIBRARY mcc)
 add_library(${MCC_LIBRARY} INTERFACE ${MCC_LIBRARY_SRC})
 target_compile_features(${MCC_LIBRARY} INTERFACE cxx_std_23)
+target_include_directories(${MCC_LIBRARY} INTERFACE ${FITPACK_INCLUDE_DIR})
 
 set(MOUNT_SERVER_APP_SRC mount.h mount_state.h mount_server.cpp comm_server.h comm_server_endpoint.h comm_server_configfile.h mount_astrom.h
     mount_astrom_default.h mcc_coord.h mount_pz.h mcc_fsm.h mcc_fsm_utils.h)
diff --git a/cxx/mcc_mount_pec.h b/cxx/mcc_mount_pec.h
index 8df50ba..ab1ddb2 100644
--- a/cxx/mcc_mount_pec.h
+++ b/cxx/mcc_mount_pec.h
@@ -1,3 +1,4 @@
+
 #pragma once
 
 
@@ -17,12 +18,11 @@ namespace mcc
 namespace traits
 {
 
-template <typename T>
-concept mcc_mount_pec_c = requires(T t) {
+template <typename T, typename XT, typename YT>
+concept mcc_mount_pec_c = requires(T t, XT x, YT y) {
     typename T::pec_result_t;
 
-    []<std::derived_from<MccAngle> XT, std::derived_from<MccAngle> YT>(const XT & x, const YT & y, T inst) ->
-        typename T::pec_result_t { return inst.compute(x, y); }(t);
+    { t.compute(std::declval<const XT&>(), std::declval<const YT&>()) } -> std::same_as<typename T::pec_result_t>;
 };
 
 }  // namespace traits