--- a/taskcluster/ci/test/mochitest.yml
+++ b/taskcluster/ci/test/mochitest.yml
@@ -437,16 +437,17 @@ mochitest-plain-headless:
     description: "Mochitest plain headless run"
     suite: mochitest/plain-chunked
     treeherder-symbol: tc-M(h)
     loopback-video: true
     instance-size: legacy # Bug 1281241: migrating to m3.large instances
     chunks:
         by-test-platform:
             linux.*: 10
+            windows.*: 5
     e10s: true
     max-run-time: 5400
     allow-software-gl-layers: false
     tier: default
     mozharness:
         mochitest-flavor: plain
         script: desktop_unittest.py
         no-read-buildbot-config: true

--- a/taskcluster/ci/test/test-platforms.yml
+++ b/taskcluster/ci/test/test-platforms.yml
@@ -209,25 +209,27 @@ windows7-32-devedition/opt:
         - windows-reftest-gpu
         - windows-tests
 
 # win64
 windows10-64/debug:
     build-platform: win64/debug
     test-sets:
         - windows-tests
+        - mochitest-headless
 
 windows10-64/opt:
     build-platform: win64/opt
     test-sets:
         - awsy
         - desktop-screenshot-capture
         - windows-talos
         - windows-talos-stylo-disabled
         - windows-tests
+        - mochitest-headless
 
 windows10-64-pgo/opt:
     build-platform: win64-pgo/opt
     test-sets:
         - awsy
         - desktop-screenshot-capture
         - windows-talos
         - windows-talos-stylo-disabled