diff --git a/BoostDetectToolset.cmake b/BoostDetectToolset.cmake
index 4ce9f8d..1e340e2 100644
--- a/BoostDetectToolset.cmake
+++ b/BoostDetectToolset.cmake
@@ -2,6 +2,9 @@
 # Distributed under the Boost Software License, Version 1.0.
 # (See accompanying file LICENSE_1_0.txt or copy at http://boost.org/LICENSE_1_0.txt)
 
+if(NOT CMAKE_CXX_COMPILER_VERSION)
+  message(FATAL_ERROR: "CMAKE_CXX_COMPILER_VERSION is not set!")
+endif()
 string(REGEX MATCHALL "[0-9]+" _BOOST_COMPILER_VERSION ${CMAKE_CXX_COMPILER_VERSION})
 
 list(GET _BOOST_COMPILER_VERSION 0 _BOOST_COMPILER_VERSION_MAJOR)