diff --git a/README.md b/README.md
index 6f05eb3..78c6f0e 100644
--- a/README.md
+++ b/README.md
@@ -58,3 +58,14 @@ Here is how it looks like in practice:
     );
 }
 ```
+
+## Known issues
+
+```
+$ nix flake check
+warning: unknown flake output 'lib'
+```
+
+nixpkgs is currently having the same issue so I assume that it will be
+eventually standardized.
+