2 files changed, 12 insertions, 3 deletions
diff --git a/tests/ui/const-generics/generic_const_exprs/opaque_type.rs b/tests/ui/const-generics/generic_const_exprs/opaque_type.rs
index 56b8acbf88c..7209290a36e 100644
--- a/tests/ui/const-generics/generic_const_exprs/opaque_type.rs
+++ b/tests/ui/const-generics/generic_const_exprs/opaque_type.rs
@@ -2,6 +2,7 @@
 #![allow(incomplete_features)]
 
 type Foo = impl Sized;
+//~^ ERROR: unconstrained opaque type
 
 fn with_bound<const N: usize>() -> Foo
 where
diff --git a/tests/ui/const-generics/generic_const_exprs/opaque_type.stderr b/tests/ui/const-generics/generic_const_exprs/opaque_type.stderr
index e9fb8c0f403..c7a266205b4 100644
--- a/tests/ui/const-generics/generic_const_exprs/opaque_type.stderr
+++ b/tests/ui/const-generics/generic_const_exprs/opaque_type.stderr
@@ -1,5 +1,5 @@
 error[E0308]: mismatched types
-  --> $DIR/opaque_type.rs:10:17
+  --> $DIR/opaque_type.rs:11:17
    |
 LL | type Foo = impl Sized;
    |            ---------- the found opaque type
@@ -11,12 +11,20 @@ LL |     let _: [u8; (N / 2) as Foo] = [0; (N / 2) as usize];
            found opaque type `Foo`
 
 error[E0605]: non-primitive cast: `usize` as `Foo`
-  --> $DIR/opaque_type.rs:10:17
+  --> $DIR/opaque_type.rs:11:17
    |
 LL |     let _: [u8; (N / 2) as Foo] = [0; (N / 2) as usize];
    |                 ^^^^^^^^^^^^^^ an `as` expression can only be used to convert between primitive types or to coerce to a specific trait object
 
-error: aborting due to 2 previous errors
+error: unconstrained opaque type
+  --> $DIR/opaque_type.rs:4:12
+   |
+LL | type Foo = impl Sized;
+   |            ^^^^^^^^^^
+   |
+   = note: `Foo` must be used in combination with a concrete type within the same module
+
+error: aborting due to 3 previous errors
 
 Some errors have detailed explanations: E0308, E0605.
 For more information about an error, try `rustc --explain E0308`.