diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 0332670..baf8c46 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -34,6 +34,8 @@ jobs:
           # older versions need older OS
           - python-version: 3.5
             os: ubuntu-20.04
+            env:
+              PIP_TRUSTED_HOST: "pypi.python.org pypi.org files.pythonhosted.org"
           - python-version: 3.6
             os: ubuntu-20.04