diff --git a/compiler/rustc_infer/src/infer/opaque_types.rs b/compiler/rustc_infer/src/infer/opaque_types.rs
index 35104c71bfc98..46420fbe0c305 100644
--- a/compiler/rustc_infer/src/infer/opaque_types.rs
+++ b/compiler/rustc_infer/src/infer/opaque_types.rs
@@ -82,7 +82,14 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
             let process = |a: Ty<'tcx>, b: Ty<'tcx>| match *a.kind() {
                 ty::Opaque(def_id, substs) => {
                     if let ty::Opaque(did2, _) = *b.kind() {
-                        if self.opaque_type_origin(did2, cause.span).is_some() {
+                        // We could accept this, but there are various ways to handle this situation, and we don't
+                        // want to make a decision on it right now. Likely this case is so super rare anyway, that
+                        // no one encounters it in practice.
+                        // It does occur however in `fn fut() -> impl Future<Output = i32> { async { 42 } }`,
+                        // where it is of no concern, so we only check for TAITs.
+                        if let Some(OpaqueTyOrigin::TyAlias) =
+                            self.opaque_type_origin(did2, cause.span)
+                        {
                             self.tcx
                                 .sess
                                 .struct_span_err(
diff --git a/src/test/ui/impl-trait/example-calendar.rs b/src/test/ui/impl-trait/example-calendar.rs
index 26618eec1d712..45dcb74a6e05c 100644
--- a/src/test/ui/impl-trait/example-calendar.rs
+++ b/src/test/ui/impl-trait/example-calendar.rs
@@ -1,3 +1,4 @@
+// run-pass
 // ignore-compare-mode-chalk
 
 #![feature(fn_traits,
@@ -589,7 +590,7 @@ fn test_format_month() {
 fn format_months(it: impl Iterator<Item = impl DateIterator>)
                 -> impl Iterator<Item=impl Iterator<Item=String>>
 {
-    it.map(format_month) //~ ERROR opaque type's hidden type cannot be another opaque type
+    it.map(format_month)
 }
 
 /// Takes an iterator of iterators of strings; the sub-iterators are consumed
diff --git a/src/test/ui/impl-trait/example-calendar.stderr b/src/test/ui/impl-trait/example-calendar.stderr
deleted file mode 100644
index 3894285947fec..0000000000000
--- a/src/test/ui/impl-trait/example-calendar.stderr
+++ /dev/null
@@ -1,19 +0,0 @@
-error: opaque type's hidden type cannot be another opaque type from the same scope
-  --> $DIR/example-calendar.rs:592:5
-   |
-LL |     it.map(format_month)
-   |     ^^^^^^^^^^^^^^^^^^^^ one of the two opaque types used here has to be outside its defining scope
-   |
-note: opaque type whose hidden type is being assigned
-  --> $DIR/example-calendar.rs:560:43
-   |
-LL | fn format_month(it: impl DateIterator) -> impl Iterator<Item=String> {
-   |                                           ^^^^^^^^^^^^^^^^^^^^^^^^^^
-note: opaque type being used as hidden type
-  --> $DIR/example-calendar.rs:590:39
-   |
-LL |                 -> impl Iterator<Item=impl Iterator<Item=String>>
-   |                                       ^^^^^^^^^^^^^^^^^^^^^^^^^^
-
-error: aborting due to previous error
-