diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 025cb0ed8..5529ea7f7 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -3,7 +3,10 @@ This document describes the way you can contribute to the restic project.
 Ways to Help Out
 ================
 
-Thank you for your contribution!
+Thank you for your contribution! Please **open an issue first** (or add a
+comment to an existing issue) if you plan to work on any code or add a new
+feature. This way, duplicate work is prevented and we can discuss your ideas
+and design first.
 
 There are several ways you can help us out. First of all code contributions and
 bug fixes are most welcome. However even "minor" details as fixing spelling
diff --git a/README.md b/README.md
index a837b442f..86459354c 100644
--- a/README.md
+++ b/README.md
@@ -40,10 +40,15 @@ Building restic with gccgo may work, but is not supported.
 Contribute and Documentation
 ============================
 
-Contributions are welcome! More information and a description of the
-development environment can be found in [`CONTRIBUTING.md`](CONTRIBUTING.md). A
-document describing the design of restic and the data structures stored on the
-back end is contained in [`doc/Design.md`](doc/Design.md).
+Contributions are welcome! Please **open an issue first** (or add a comment to
+an existing issue) if you plan to work on any code or add a new feature. This
+way, duplicate work is prevented and we can discuss your ideas and design
+first.
+
+More information and a description of the development environment can be found
+in [`CONTRIBUTING.md`](CONTRIBUTING.md). A document describing the design of
+restic and the data structures stored on the back end is contained in
+[`doc/Design.md`](doc/Design.md).
 
 If you'd like to start contributing to restic, but don't know exactly what do
 to, have a look at this great article by Dave Cheney: