diff --git a/unittest/force-styles/CMakeLists.txt b/unittest/force-styles/CMakeLists.txt
index 89cfef45cb..043b628fd3 100644
--- a/unittest/force-styles/CMakeLists.txt
+++ b/unittest/force-styles/CMakeLists.txt
@@ -64,7 +64,7 @@ endif()
 
 # prepare environment for testers
 if(WIN32)
-  set(FORCE_TEST_ENVIRONMENT PYTHONPATH="${TEST_INPUT_FOLDER}")
+  set(FORCE_TEST_ENVIRONMENT PYTHONPATH=${TEST_INPUT_FOLDER})
 else()
   set(FORCE_TEST_ENVIRONMENT PYTHONPATH=${TEST_INPUT_FOLDER}:${LAMMPS_PYTHON_DIR}:$ENV{PYTHONPATH})
 endif()