diff --git a/unittest/python/CMakeLists.txt b/unittest/python/CMakeLists.txt
index 881c18423d..7eeba268e5 100644
--- a/unittest/python/CMakeLists.txt
+++ b/unittest/python/CMakeLists.txt
@@ -40,6 +40,7 @@ endif()
 list(APPEND PYTHON_TEST_ENVIRONMENT "LAMMPS_POTENTIALS=${LAMMPS_POTENTIALS_DIR}")
 list(APPEND PYTHON_TEST_ENVIRONMENT "PYTHONUNBUFFERED=1")
 list(APPEND PYTHON_TEST_ENVIRONMENT "PYTHONDONTWRITEBYTECODE=1")
+list(APPEND PYTHON_TEST_ENVIRONMENT "OMP_NUM_THREADS=1")
 if(APPLE)
   list(APPEND PYTHON_TEST_ENVIRONMENT "DYLD_LIBRARY_PATH=${LAMMPS_LIB_PATH}:$ENV{DYLD_LIBRARY_PATH}")
 elseif(WIN32)