diff --git a/cmake/Modules/EvtGenCompilerFlags.cmake b/cmake/Modules/EvtGenCompilerFlags.cmake
index bc0c118..6069d73 100644
--- a/cmake/Modules/EvtGenCompilerFlags.cmake
+++ b/cmake/Modules/EvtGenCompilerFlags.cmake
@@ -1,88 +1,90 @@
 
 ########################################################################
 # Copyright 1998-2020 CERN for the benefit of the EvtGen authors       #
 #                                                                      #
 # This file is part of EvtGen.                                         #
 #                                                                      #
 # EvtGen is free software: you can redistribute it and/or modify       #
 # it under the terms of the GNU General Public License as published by #
 # the Free Software Foundation, either version 3 of the License, or    #
 # (at your option) any later version.                                  #
 #                                                                      #
 # EvtGen is distributed in the hope that it will be useful,            #
 # but WITHOUT ANY WARRANTY; without even the implied warranty of       #
 # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the        #
 # GNU General Public License for more details.                         #
 #                                                                      #
 # You should have received a copy of the GNU General Public License    #
 # along with EvtGen.  If not, see <https://www.gnu.org/licenses/>.     #
 ########################################################################
 
 
 # Set the build type (if not already specified)
 if(NOT CMAKE_BUILD_TYPE AND NOT CMAKE_CONFIGURATION_TYPES)
     message(STATUS "EvtGen: Setting build type to 'Release' as none was specified")
     set(CMAKE_BUILD_TYPE "Release" CACHE STRING "Choose the type of build, options are: Release, MinSizeRel, Debug, RelWithDebInfo" FORCE)
     set_property(CACHE CMAKE_BUILD_TYPE PROPERTY STRINGS "Debug" "Release" "MinSizeRel" "RelWithDebInfo")
 elseif(CMAKE_BUILD_TYPE AND NOT CMAKE_CONFIGURATION_TYPES)
     message(STATUS "EvtGen: Build type '${CMAKE_BUILD_TYPE}'")
 endif()
 
 # Set the warning/optimise/debug flags for each build type
 if( ${CMAKE_CXX_COMPILER_ID} STREQUAL "GNU" OR ${CMAKE_CXX_COMPILER_ID} MATCHES "Clang" )
     message(STATUS "EvtGen: Customising compiler flags for each build type")
 
     #set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fsigned-char -Wall -Wextra -Wshadow -Woverloaded-virtual")
     set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fsigned-char -Wall -Wextra")
 
     if( ${CMAKE_CXX_COMPILER_ID} STREQUAL "GNU" )
         set(CMAKE_CXX_FLAGS_DEBUG          "-Og -g3")
         set(CMAKE_CXX_FLAGS_MINSIZEREL     "-Os -DNDEBUG")
         set(CMAKE_CXX_FLAGS_RELEASE        "-O3 -DNDEBUG")
         set(CMAKE_CXX_FLAGS_RELWITHDEBINFO "-O2 -g3")
     elseif( ${CMAKE_CXX_COMPILER_ID} MATCHES "Clang" )
         set(CMAKE_CXX_FLAGS_DEBUG          "-O0 -g")
         set(CMAKE_CXX_FLAGS_MINSIZEREL     "-Os -DNDEBUG")
         set(CMAKE_CXX_FLAGS_RELEASE        "-O3 -DNDEBUG")
         set(CMAKE_CXX_FLAGS_RELWITHDEBINFO "-O2 -g")
     endif()
 else()
     message(STATUS "EvtGen: No customisation of compiler flags implemented for compiler: ${CMAKE_CXX_COMPILER_ID}")
 endif()
 
 # Make sure our project's include directories always come first
 set(CMAKE_INCLUDE_DIRECTORIES_PROJECT_BEFORE ON)
 
 # Prioritise UNIX-style packages over macOS frameworks
 set(CMAKE_FIND_FRAMEWORK LAST)
 
 # Control verbosity of the build
 set(CMAKE_VERBOSE_MAKEFILE OFF CACHE BOOL "Control verbosity of generated Makefiles")
 
 # Control verbosity of the install - suppresses 'up-to-date' messages
 set(CMAKE_INSTALL_MESSAGE LAZY)
 
 # C++ standard settings
 set(CMAKE_CXX_EXTENSIONS OFF)
 set(EVTGEN_CXX_STANDARD 17)
 if(DEFINED ENV{CMAKE_CXX_STANDARD})
     if($ENV{CMAKE_CXX_STANDARD} GREATER ${EVTGEN_CXX_STANDARD})
         set(EVTGEN_CXX_STANDARD $ENV{CMAKE_CXX_STANDARD})
+    elseif($ENV{CMAKE_CXX_STANDARD} LESS ${EVTGEN_CXX_STANDARD})
+        message(WARNING "EvtGen: Version of C++ standard requested via CMAKE_CXX_STANDARD environment variable, C++$ENV{CMAKE_CXX_STANDARD}, is below required minimum of C++${EVTGEN_CXX_STANDARD}, not changing it")
     endif()
 endif()
 set(CMAKE_CXX_STANDARD ${EVTGEN_CXX_STANDARD} CACHE STRING "C++ standard")
 set(CMAKE_CXX_STANDARD_REQUIRED ON)
 message(STATUS "EvtGen: Using C++${CMAKE_CXX_STANDARD} standard")
 
 # Special linker flags for MacOSX
 if (APPLE)
     set(CMAKE_SHARED_LINKER_FLAGS "${CMAKE_SHARED_LINKER_FLAGS} -single_module -undefined dynamic_lookup")
 endif()
 
 # RPATH handling
 set(CMAKE_MACOSX_RPATH TRUE)
 set(CMAKE_SKIP_BUILD_RPATH FALSE)
 set(CMAKE_BUILD_WITH_INSTALL_RPATH FALSE)
 set(CMAKE_INSTALL_RPATH "${CMAKE_INSTALL_PREFIX}/${CMAKE_INSTALL_LIBDIR}")
 set(CMAKE_INSTALL_RPATH_USE_LINK_PATH TRUE)