diff --git a/Dangerfile b/Dangerfile
index dafaaa3..ec04c4e 100644
--- a/Dangerfile
+++ b/Dangerfile
@@ -1,3 +1,9 @@
+# Contributors should write up some reasoning about the PR, rather than just leave a title
 if github.pr_body.length < 5
   fail "Please provide a summary in the Pull Request description"
 end
+
+# Ensure a clean commits history
+if git.commits.any? { |c| c.message =~ /^Merge branch '#{github.branch_for_base}'/ }
+  fail('Please rebase to get rid of the merge commits in this PR')
+end