diff --git a/.ci/dockerfiles/fed-build/Dockerfile b/.ci/dockerfiles/fed-build/Dockerfile
index 00de57cfb..584e2376d 100644
--- a/.ci/dockerfiles/fed-build/Dockerfile
+++ b/.ci/dockerfiles/fed-build/Dockerfile
@@ -1,2 +1,3 @@
-FROM fedora:latest
+# mock on Fedora 40 seems broken, so stick with 39 for now
+FROM fedora:39
 RUN dnf -y --enablerepo='updates-testing' install mock git rpm-build rpmdevtools && dnf clean all