diff --git a/doc/05-repositories.md b/doc/05-repositories.md
index 2dd5e24d5..3b0bd4d38 100644
--- a/doc/05-repositories.md
+++ b/doc/05-repositories.md
@@ -234,7 +234,7 @@ project to use the patched version. If the library is on GitHub (this is the
 case most of the time), you can simply fork it there and push your changes to
 your fork. After that you update the project's `composer.json`. All you have
 to do is add your fork as a repository and update the version constraint to
-point to your custom branch. For version constraint naming conventions see
+point to your custom branch. Your custom branch name must be prefixed with `"dev-"`. For version constraint naming conventions see
 [Libraries](02-libraries.md) for more information.
 
 Example assuming you patched monolog to fix a bug in the `bugfix` branch: