--- a/taskcluster/ci/test/tests.yml
+++ b/taskcluster/ci/test/tests.yml
@@ -1180,17 +1180,17 @@ reftest-no-accel:
             linux64-jsdcov/opt: false
             windows7-32/debug: both
             default: true
     mozharness:
         script: desktop_unittest.py
         no-read-buildbot-config: true
         chunked:
             by-test-platform:
-                windows8-64.*/opt: true
+                windows8-64.*/opt: false
                 macosx.*: false
                 default: true
         config:
             by-test-platform:
                 windows.*:
                     - unittests/win_taskcluster_unittest.py
                 macosx.*:
                     - unittests/mac_unittest.py