diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 3bbe74bc..e8b9c92f 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -10,3 +10,5 @@ Prometheus uses GitHub to manage reviews of pull requests.
   on our [mailing list](https://groups.google.com/forum/?fromgroups#!forum/prometheus-developers).
   This will avoid unnecessary work and surely give you and us a good deal
   of inspiration.
+ 
+* Be sure to sign off on the [DCO](https://github.com/probot/dco#how-it-works)