diff --git a/docs/Mtl-2.3.x-Migration.md b/docs/Mtl-2.3.x-Migration.md
index e2a7af0..4cd7c72 100644
--- a/docs/Mtl-2.3.x-Migration.md
+++ b/docs/Mtl-2.3.x-Migration.md
@@ -25,7 +25,7 @@ packages: .
 source-repository-package
   type: git
   location: https://github.com/haskell/mtl
-  tag: 2.3.1
+  tag: v2.3.1
 
 allow-newer:
   *:mtl