Index: cadabra2-2.2.0/CMakeLists.txt
===================================================================
--- cadabra2-2.2.0.orig/CMakeLists.txt
+++ cadabra2-2.2.0/CMakeLists.txt
@@ -80,7 +80,7 @@ debug_message("Initial compiler flags: $
 
 # GCC
 if(CMAKE_COMPILER_IS_GNUCC OR CMAKE_COMPILER_IS_GNUCXX)
-  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -g -O2 -Wall -Wno-unused-but-set-variable")
+  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -g -O2 -Wall -Wno-unused-but-set-variable -pthread")
 endif()
 
 # Clang