diff --git a/.readthedocs.yml b/.readthedocs.yml
index 49da59e2..029e73dd 100644
--- a/.readthedocs.yml
+++ b/.readthedocs.yml
@@ -9,6 +9,13 @@ build:
   jobs:
     post_checkout:
       - git fetch --unshallow
+      # Use -W builds for PRs
+      - |
+        if [[ "$READTHEDOCS_VERSION_NAME" =~ ^[0-9]+$ ]]; then
+            export SPHINXOPTS="-W"
+        fi
+      - env
+    pre_build:
       - env
 
 python: