Index: cadabra2-2.2.5/CMakeLists.txt
===================================================================
--- cadabra2-2.2.5.orig/CMakeLists.txt
+++ cadabra2-2.2.5/CMakeLists.txt
@@ -104,7 +104,7 @@ if(CMAKE_COMPILER_IS_GNUCC OR CMAKE_COMP
 			message(FATAL_ERROR "GCC version must be at least 4.9 for regex support! See http://askubuntu.com/questions/428198/getting-installing-gcc-g-4-9-on-ubuntu and then set the environment variables CXX to g++-4.9 and CC to gcc-4.9. You may have to erase the build directory before re-running cmake.")
 		endif()
 	endif()
-	set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -g -O2 -Wall -fvisibility=hidden -Wno-unused-but-set-variable")
+	set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -g -O2 -Wall -fvisibility=hidden -Wno-unused-but-set-variable -pthread")
 endif()
 
 # Clang