diff -ruN -x '*~' -x '*.o' -x '*.a' -x '*.so' -x '*.so.[0-9]' -x autom4te.cache -x .deps -x .libs ../orig-cadabra2-2.1.7/CMakeLists.txt ./CMakeLists.txt
--- ../orig-cadabra2-2.1.7/CMakeLists.txt	2017-11-19 20:27:27.000000000 +0100
+++ ./CMakeLists.txt	2017-12-29 09:34:50.496366051 +0100
@@ -202,7 +202,7 @@
 include(CPack)
 
 if(CMAKE_COMPILER_IS_GNUCC OR CMAKE_COMPILER_IS_GNUCXX)
-   set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11 -O2")
+   set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11 -O2 -pthread")
 endif()
 
 if("${CMAKE_CXX_COMPILER_ID}" STREQUAL "Clang")