diff --git a/compiler/rustc_mir/src/borrow_check/region_infer/opaque_types.rs b/compiler/rustc_mir/src/borrow_check/region_infer/opaque_types.rs
index 0d1d255104272..5a334ed556d01 100644
--- a/compiler/rustc_mir/src/borrow_check/region_infer/opaque_types.rs
+++ b/compiler/rustc_mir/src/borrow_check/region_infer/opaque_types.rs
@@ -60,33 +60,17 @@ impl<'tcx> RegionInferenceContext<'tcx> {
                 debug!(?concrete_type, ?substs);
 
                 let mut subst_regions = vec![self.universal_regions.fr_static];
-                let universal_substs =
-                    infcx.tcx.fold_regions(substs, &mut false, |region, _| match *region {
-                        ty::ReVar(vid) => {
-                            subst_regions.push(vid);
-                            self.definitions[vid].external_name.unwrap_or_else(|| {
-                                infcx.tcx.sess.delay_span_bug(
-                                    span,
-                                    "opaque type with non-universal region substs",
-                                );
-                                infcx.tcx.lifetimes.re_static
-                            })
-                        }
-                        // We don't fold regions in the predicates of opaque
-                        // types to `ReVar`s. This means that in a case like
-                        //
-                        // fn f<'a: 'a>() -> impl Iterator<Item = impl Sized>
-                        //
-                        // The inner opaque type has `'static` in its substs.
-                        ty::ReStatic => region,
-                        _ => {
-                            infcx.tcx.sess.delay_span_bug(
-                                span,
-                                &format!("unexpected concrete region in borrowck: {:?}", region),
-                            );
-                            region
-                        }
-                    });
+                let universal_substs = infcx.tcx.fold_regions(substs, &mut false, |region, _| {
+                    let vid = self.universal_regions.to_region_vid(region);
+                    subst_regions.push(vid);
+                    self.definitions[vid].external_name.unwrap_or_else(|| {
+                        infcx
+                            .tcx
+                            .sess
+                            .delay_span_bug(span, "opaque type with non-universal region substs");
+                        infcx.tcx.lifetimes.re_static
+                    })
+                });
 
                 subst_regions.sort();
                 subst_regions.dedup();
diff --git a/src/test/ui/type-alias-impl-trait/associated-type-lifetime-ice.rs b/src/test/ui/type-alias-impl-trait/associated-type-lifetime-ice.rs
deleted file mode 100644
index 967d4c3f0f7f9..0000000000000
--- a/src/test/ui/type-alias-impl-trait/associated-type-lifetime-ice.rs
+++ /dev/null
@@ -1,33 +0,0 @@
-// failure-status: 101
-// rustc-env:RUST_BACKTRACE=0
-// normalize-stderr-test "note: .*\n\n" -> ""
-// normalize-stderr-test "thread 'rustc' panicked.*\n" -> ""
-
-// compile-flags: --crate-type=rlib
-
-// Regression test for https://github.com/rust-lang/rust/issues/78450
-
-#![feature(min_type_alias_impl_trait)]
-#![no_std]
-
-pub trait AssociatedImpl {
-    type ImplTrait;
-
-    fn f() -> Self::ImplTrait;
-}
-
-struct S<T>(T);
-
-trait Associated {
-    type A;
-}
-
-// ICE
-impl<'a, T: Associated<A = &'a ()>> AssociatedImpl for S<T> {
-    type ImplTrait = impl core::fmt::Debug;
-
-    fn f() -> Self::ImplTrait {
-    //~^ ERROR unexpected concrete region in borrowck: ReEarlyBound(0, 'a)
-        ()
-    }
-}
diff --git a/src/test/ui/type-alias-impl-trait/associated-type-lifetime-ice.stderr b/src/test/ui/type-alias-impl-trait/associated-type-lifetime-ice.stderr
deleted file mode 100644
index 64ab7b70b1a98..0000000000000
--- a/src/test/ui/type-alias-impl-trait/associated-type-lifetime-ice.stderr
+++ /dev/null
@@ -1,13 +0,0 @@
-error: internal compiler error: unexpected concrete region in borrowck: ReEarlyBound(0, 'a)
-  --> $DIR/associated-type-lifetime-ice.rs:29:5
-   |
-LL | /     fn f() -> Self::ImplTrait {
-LL | |
-LL | |         ()
-LL | |     }
-   | |_____^
-   |
-   = error: internal compiler error: unexpected panic
-
-query stack during panic:
-end of query stack
diff --git a/src/test/ui/type-alias-impl-trait/issue-78450.rs b/src/test/ui/type-alias-impl-trait/issue-78450.rs
new file mode 100644
index 0000000000000..640f929f8f11b
--- /dev/null
+++ b/src/test/ui/type-alias-impl-trait/issue-78450.rs
@@ -0,0 +1,27 @@
+// check-pass
+
+#![feature(min_type_alias_impl_trait)]
+#![feature(type_alias_impl_trait)]
+//~^ WARNING: the feature `type_alias_impl_trait` is incomplete
+
+pub trait AssociatedImpl {
+    type ImplTrait;
+
+    fn f() -> Self::ImplTrait;
+}
+
+struct S<T>(T);
+
+trait Associated {
+    type A;
+}
+
+impl<'a, T: Associated<A = &'a ()>> AssociatedImpl for S<T> {
+    type ImplTrait = impl core::fmt::Debug;
+
+    fn f() -> Self::ImplTrait {
+        ()
+    }
+}
+
+fn main() {}
diff --git a/src/test/ui/type-alias-impl-trait/issue-78450.stderr b/src/test/ui/type-alias-impl-trait/issue-78450.stderr
new file mode 100644
index 0000000000000..efccf6241fb78
--- /dev/null
+++ b/src/test/ui/type-alias-impl-trait/issue-78450.stderr
@@ -0,0 +1,11 @@
+warning: the feature `type_alias_impl_trait` is incomplete and may not be safe to use and/or cause compiler crashes
+  --> $DIR/issue-78450.rs:4:12
+   |
+LL | #![feature(type_alias_impl_trait)]
+   |            ^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: `#[warn(incomplete_features)]` on by default
+   = note: see issue #63063 <https://github.com/rust-lang/rust/issues/63063> for more information
+
+warning: 1 warning emitted
+