diff --git a/scripts/nightly.yaml b/scripts/nightly.yaml
index 96ef85ebc..e8175a3df 100644
--- a/scripts/nightly.yaml
+++ b/scripts/nightly.yaml
@@ -36,7 +36,7 @@ stages:
   - job: UbuntoDoc
     displayName: "Ubuntu Doc build"
     pool:
-      vmImage: "ubuntu-latest"
+      vmImage: "Ubuntu-18.04"
     steps:
     - script: sudo apt-get install ocaml opam libgmp-dev
     - script: sudo apt-get install doxygen