diff --git a/src/subtyping.md b/src/subtyping.md
index 15b0b206a..e209d6a1c 100644
--- a/src/subtyping.md
+++ b/src/subtyping.md
@@ -83,6 +83,8 @@ struct Variance<'a, 'b, T, U: 'a> {
 }
 ```
 
+To debug variance of custom struct, see `src/test/ui/variance/variance-types.rs`.
+
 [function pointers]: types/function-pointer.md
 [Higher-ranked]: ../nomicon/hrtb.html
 [trait objects]: types/trait-object.md