diff --git a/compiler/rustc_ty_utils/src/layout.rs b/compiler/rustc_ty_utils/src/layout.rs
index bebc0707e26d..5a41e46f3a6b 100644
--- a/compiler/rustc_ty_utils/src/layout.rs
+++ b/compiler/rustc_ty_utils/src/layout.rs
@@ -777,7 +777,9 @@ fn layout_of_uncached<'tcx>(
             let err = if ty.has_param() || !cx.typing_env.param_env.caller_bounds().is_empty() {
                 LayoutError::TooGeneric(ty)
             } else {
-                unreachable!("invalid rigid alias in layout_of after normalization: {ty:?}");
+                LayoutError::ReferencesError(cx.tcx().dcx().delayed_bug(format!(
+                    "unexpected rigid alias in layout_of after normalization: {ty:?}"
+                )))
             };
             return Err(error(cx, err));
         }
diff --git a/tests/ui/layout/rigid-alias-due-to-broken-impl.stderr b/tests/ui/layout/rigid-alias-due-to-broken-impl.stderr
new file mode 100644
index 000000000000..e9ba6df2fdc7
--- /dev/null
+++ b/tests/ui/layout/rigid-alias-due-to-broken-impl.stderr
@@ -0,0 +1,12 @@
+error[E0046]: not all trait items implemented, missing: `Assoc`
+  --> $DIR/rigid-alias-due-to-broken-impl.rs:14:1
+   |
+LL |     type Assoc;
+   |     ---------- `Assoc` from trait
+...
+LL | impl Foo for str {}
+   | ^^^^^^^^^^^^^^^^ missing `Assoc` in implementation
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0046`.