diff --git a/circle.yml b/circle.yml
index 4ce3082bf..5df0609e8 100644
--- a/circle.yml
+++ b/circle.yml
@@ -213,10 +213,19 @@ jobs:
           path: docs/_build/html/
           destination: docs-html
 
+  merge_blocker:
+    docker:
+      - image: buildpack-deps:artful
+    steps:
+      - run:
+          name: This blocks the merge. Remove when 0.5.0 is to be released.
+          command: false
+
 workflows:
   version: 2
   build_all:
     jobs:
+      - merge_blocker
       - build_emscripten: *build_on_tags
       - test_emscripten_solcjs:
           <<: *build_on_tags