diff --git a/hbp_nrp_distributed_nest/requirements_extension_tests.txt b/hbp_nrp_distributed_nest/requirements_extension_tests.txt
index 076fef2e3af5bd4dffad43891493047eebb92bab..ce35c3868f08d2d9bdf3f857a2648722e99046d8 100644
--- a/hbp_nrp_distributed_nest/requirements_extension_tests.txt
+++ b/hbp_nrp_distributed_nest/requirements_extension_tests.txt
@@ -1,3 +1,3 @@
 #the following is required for the unit testing
-mock==1.0.1
+mock==1.0.1; python_version < "3.3"
 testfixtures