diff --git a/ThunkLibs/Generator/main.cpp b/ThunkLibs/Generator/main.cpp
index 726e5cbfa4..d238fc1ea1 100644
--- a/ThunkLibs/Generator/main.cpp
+++ b/ThunkLibs/Generator/main.cpp
@@ -77,6 +77,7 @@ int main(int argc, char* const argv[]) {
             AdjustedArgs.push_back(std::string { "--target=" } + platform + "-linux-unknown");
             AdjustedArgs.push_back("-isystem");
             AdjustedArgs.push_back(std::string { "/usr/" } + platform + "-linux-gnu/include/");
+            AdjustedArgs.push_back("-DGUEST_THUNK_LIBRARY");
             return AdjustedArgs;
         };
         GuestTool.appendArgumentsAdjuster(append_guest_args);
diff --git a/ThunkLibs/GuestLibs/CMakeLists.txt b/ThunkLibs/GuestLibs/CMakeLists.txt
index d32266516c..62cb78c430 100644
--- a/ThunkLibs/GuestLibs/CMakeLists.txt
+++ b/ThunkLibs/GuestLibs/CMakeLists.txt
@@ -51,7 +51,6 @@ function(generate NAME SOURCE_FILE)
   # Interface target for the user to add include directories
   add_library(${NAME}-guest-deps INTERFACE)
   target_include_directories(${NAME}-guest-deps INTERFACE "${CMAKE_CURRENT_SOURCE_DIR}/../include")
-  target_compile_definitions(${NAME}-guest-deps INTERFACE GUEST_THUNK_LIBRARY)
   if (BITNESS EQUAL 32)
     target_compile_definitions(${NAME}-guest-deps INTERFACE IS_32BIT_THUNK)
   endif ()
diff --git a/unittests/FEXLinuxTests/tests/thunks/thunk_testlib.cpp b/unittests/FEXLinuxTests/tests/thunks/thunk_testlib.cpp
index c1ae5c564e..183a5c31dc 100644
--- a/unittests/FEXLinuxTests/tests/thunks/thunk_testlib.cpp
+++ b/unittests/FEXLinuxTests/tests/thunks/thunk_testlib.cpp
@@ -1,3 +1,5 @@
+#define GUEST_THUNK_LIBRARY
+
 #include <dlfcn.h>
 
 #include <stdexcept>