diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 5baac08d723c5c1295cd8da9c8150645617121b2..6214aa25943225d382f88934f9aa7bfbc54c3ce0 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -6,6 +6,9 @@ test:
   script:
     - javac *.java
     - java GenerateSite
+    # heuristic to see if any lines were removed!
+    - git fetch origin main
+    - '(exit $(git diff origin/main HEAD | grep "^-[^-]" | wc -l)) || { echo "Malformed merge request: at least one line is removed in diff." && (exit 1) }'
 
 pages:
   tags: