diff --git a/.circleci/config.yml b/.circleci/config.yml
index 77b661ab9..6dbdf8ff4 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -281,6 +281,8 @@ jobs:
     environment:
       <<: *UTF_8_ENVIRONMENT
       TAHOE_LAFS_TOX_ENVIRONMENT: "py36"
+      # zfec 1.5.3 is uninstallable without a utf-8 locale
+      LC_ALL: "en_US.utf-8"
 
 
   centos-8: &RHEL_DERIV