diff --git a/compiler/rustc_ty_utils/src/ty.rs b/compiler/rustc_ty_utils/src/ty.rs
index 3eebb4ace477f..99d3bda6ebfff 100644
--- a/compiler/rustc_ty_utils/src/ty.rs
+++ b/compiler/rustc_ty_utils/src/ty.rs
@@ -413,7 +413,7 @@ fn issue33140_self_ty(tcx: TyCtxt<'_>, def_id: DefId) -> Option<Ty<'_>> {
 /// Check if a function is async.
 fn asyncness(tcx: TyCtxt<'_>, def_id: DefId) -> hir::IsAsync {
     let node = tcx.hir().get_by_def_id(def_id.expect_local());
-    if let Some(fn_kind) = node.fn_kind() { fn_kind.asyncness() } else { hir::IsAsync::NotAsync }
+    node.fn_sig().map_or(hir::IsAsync::NotAsync, |sig| sig.header.asyncness)
 }
 
 /// Don't call this directly: use ``tcx.conservative_is_privately_uninhabited`` instead.
diff --git a/src/librustdoc/clean/mod.rs b/src/librustdoc/clean/mod.rs
index ad4ad4104e104..d52b9a8e3fc62 100644
--- a/src/librustdoc/clean/mod.rs
+++ b/src/librustdoc/clean/mod.rs
@@ -880,7 +880,7 @@ fn clean_fn_or_proc_macro<'tcx>(
             ProcMacroItem(ProcMacro { kind, helpers })
         }
         None => {
-            let mut func = clean_function(cx, sig, generics, body_id);
+            let mut func = clean_function(cx, sig, generics, FunctionArgs::Body(body_id));
             clean_fn_decl_legacy_const_generics(&mut func, attrs);
             FunctionItem(func)
         }
@@ -917,16 +917,28 @@ fn clean_fn_decl_legacy_const_generics(func: &mut Function, attrs: &[ast::Attrib
     }
 }
 
+enum FunctionArgs<'tcx> {
+    Body(hir::BodyId),
+    Names(&'tcx [Ident]),
+}
+
 fn clean_function<'tcx>(
     cx: &mut DocContext<'tcx>,
     sig: &hir::FnSig<'tcx>,
     generics: &hir::Generics<'tcx>,
-    body_id: hir::BodyId,
+    args: FunctionArgs<'tcx>,
 ) -> Box<Function> {
     let (generics, decl) = enter_impl_trait(cx, |cx| {
         // NOTE: generics must be cleaned before args
         let generics = clean_generics(generics, cx);
-        let args = clean_args_from_types_and_body_id(cx, sig.decl.inputs, body_id);
+        let args = match args {
+            FunctionArgs::Body(body_id) => {
+                clean_args_from_types_and_body_id(cx, sig.decl.inputs, body_id)
+            }
+            FunctionArgs::Names(names) => {
+                clean_args_from_types_and_names(cx, sig.decl.inputs, names)
+            }
+        };
         let mut decl = clean_fn_decl_with_args(cx, sig.decl, args);
         if sig.header.is_async() {
             decl.output = decl.sugared_async_return_type();
@@ -1051,18 +1063,12 @@ fn clean_trait_item<'tcx>(trait_item: &hir::TraitItem<'tcx>, cx: &mut DocContext
             ),
             hir::TraitItemKind::Const(ty, None) => TyAssocConstItem(clean_ty(ty, cx)),
             hir::TraitItemKind::Fn(ref sig, hir::TraitFn::Provided(body)) => {
-                let m = clean_function(cx, sig, trait_item.generics, body);
+                let m = clean_function(cx, sig, trait_item.generics, FunctionArgs::Body(body));
                 MethodItem(m, None)
             }
             hir::TraitItemKind::Fn(ref sig, hir::TraitFn::Required(names)) => {
-                let (generics, decl) = enter_impl_trait(cx, |cx| {
-                    // NOTE: generics must be cleaned before args
-                    let generics = clean_generics(trait_item.generics, cx);
-                    let args = clean_args_from_types_and_names(cx, sig.decl.inputs, names);
-                    let decl = clean_fn_decl_with_args(cx, sig.decl, args);
-                    (generics, decl)
-                });
-                TyMethodItem(Box::new(Function { decl, generics }))
+                let m = clean_function(cx, sig, trait_item.generics, FunctionArgs::Names(names));
+                TyMethodItem(m)
             }
             hir::TraitItemKind::Type(bounds, Some(default)) => {
                 let generics = enter_impl_trait(cx, |cx| clean_generics(trait_item.generics, cx));
@@ -1099,7 +1105,7 @@ pub(crate) fn clean_impl_item<'tcx>(
                 AssocConstItem(clean_ty(ty, cx), default)
             }
             hir::ImplItemKind::Fn(ref sig, body) => {
-                let m = clean_function(cx, sig, impl_.generics, body);
+                let m = clean_function(cx, sig, impl_.generics, FunctionArgs::Body(body));
                 let defaultness = cx.tcx.impl_defaultness(impl_.owner_id);
                 MethodItem(m, Some(defaultness))
             }
diff --git a/src/librustdoc/clean/types.rs b/src/librustdoc/clean/types.rs
index 439311f064029..f1eb438b199ce 100644
--- a/src/librustdoc/clean/types.rs
+++ b/src/librustdoc/clean/types.rs
@@ -694,13 +694,10 @@ impl Item {
                     asyncness: hir::IsAsync::NotAsync,
                 }
             }
-            ItemKind::FunctionItem(_) | ItemKind::MethodItem(_, _) => {
+            ItemKind::FunctionItem(_) | ItemKind::MethodItem(_, _) | ItemKind::TyMethodItem(_) => {
                 let def_id = self.item_id.as_def_id().unwrap();
                 build_fn_header(def_id, tcx, tcx.asyncness(def_id))
             }
-            ItemKind::TyMethodItem(_) => {
-                build_fn_header(self.item_id.as_def_id().unwrap(), tcx, hir::IsAsync::NotAsync)
-            }
             _ => return None,
         };
         Some(header)
diff --git a/src/test/rustdoc/async-trait-sig.rs b/src/test/rustdoc/async-trait-sig.rs
new file mode 100644
index 0000000000000..2578bc8f7a166
--- /dev/null
+++ b/src/test/rustdoc/async-trait-sig.rs
@@ -0,0 +1,14 @@
+// edition:2021
+
+#![feature(async_fn_in_trait)]
+#![allow(incomplete_features)]
+
+pub trait Foo {
+    // @has async_trait_sig/trait.Foo.html '//h4[@class="code-header"]' "async fn bar() -> i32"
+    async fn bar() -> i32;
+
+    // @has async_trait_sig/trait.Foo.html '//h4[@class="code-header"]' "async fn baz() -> i32"
+    async fn baz() -> i32 {
+        1
+    }
+}