diff --git a/CMakeLists.txt b/CMakeLists.txt
index 60549b1..32b3181 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -39,7 +39,9 @@ set(CMAKE_CXX_FLAGS "-Wall -Werror -Wpedantic")
 
 
 if (UNIT_TESTING)
-
+    
+    #Allows usage of preprossor stuff in your files.
+    add_compile_definitions(UNIT_TESTING=1)
     if(DEFINED ENV{CPPUTEST_HOME})
         message(STATUS "Using CppUTest home: $ENV{CPPUTEST_HOME}")
         set(CPPUTEST_INCLUDE_DIRS $ENV{CPPUTEST_HOME}/include)