diff --git a/ci/requirements-py3.14.yml b/ci/requirements-py3.14.yml
index 1b1501c66f..db00da0c27 100644
--- a/ci/requirements-py3.14.yml
+++ b/ci/requirements-py3.14.yml
@@ -23,6 +23,7 @@ dependencies:
     - requests
     - scipy >= 1.7.2
     - statsmodels
+    - tk < 9  # tk 9.0.4 from defaults crashes micromamba on windows as of 2026-09
     - pip:
         # - nrel-pysam>=2.0  # not available for py 3.14 as of 2025-11-03
         - solarfactors