diff --git a/chapters/testing/googletest.md b/chapters/testing/googletest.md
index 5960e5e..704651f 100644
--- a/chapters/testing/googletest.md
+++ b/chapters/testing/googletest.md
@@ -64,8 +64,8 @@ macro(package_add_test TESTNAME)
     # see https://cmake.org/cmake/help/v3.10/module/GoogleTest.html for more options to pass to it
     gtest_discover_tests(${TESTNAME}
         # set a working directory so your project root so that you can find test data via paths relative to the project root
-        WORKING_DIRECTORY ${PROJECT_DIR}
-        PROPERTIES VS_DEBUGGER_WORKING_DIRECTORY "${PROJECT_DIR}"
+        WORKING_DIRECTORY ${PROJECT_SOURCE_DIR}
+        PROPERTIES VS_DEBUGGER_WORKING_DIRECTORY "${PROJECT_SOURCE_DIR}"
     )
     set_target_properties(${TESTNAME} PROPERTIES FOLDER tests)
 endmacro()