diff --git a/gcc/rust/checks/errors/rust-ast-validation.cc b/gcc/rust/checks/errors/rust-ast-validation.cc
index b50e9cdf8581..0ed5d0608943 100644
--- a/gcc/rust/checks/errors/rust-ast-validation.cc
+++ b/gcc/rust/checks/errors/rust-ast-validation.cc
@@ -141,9 +141,16 @@ ASTValidation::visit (AST::TraitFunctionDecl &decl)
 {
   const auto &qualifiers = decl.get_qualifiers ();
 
-  if (context.back () == Context::TRAIT && qualifiers.is_const ())
-    rust_error_at (decl.get_identifier ().get_locus (), ErrorCode::E0379,
-		   "functions in traits cannot be declared const");
+  if (context.back () == Context::TRAIT)
+    {
+      // may change soon
+      if (qualifiers.is_async ())
+	rust_error_at (decl.get_identifier ().get_locus (), ErrorCode::E0706,
+		       "functions in traits cannot be declared %<async%>");
+      if (qualifiers.is_const ())
+	rust_error_at (decl.get_identifier ().get_locus (), ErrorCode::E0379,
+		       "functions in traits cannot be declared const");
+    }
 }
 
 void
diff --git a/gcc/rust/parse/rust-parse-impl.h b/gcc/rust/parse/rust-parse-impl.h
index 872c1fae2a3b..54885221e18d 100644
--- a/gcc/rust/parse/rust-parse-impl.h
+++ b/gcc/rust/parse/rust-parse-impl.h
@@ -5096,6 +5096,7 @@ Parser<ManagedTokenSource>::parse_trait_item ()
       // else, fallthrough to function
       // TODO: find out how to disable gcc "implicit fallthrough" error
       gcc_fallthrough ();
+    case ASYNC:
     case UNSAFE:
     case EXTERN_KW:
       case FN_KW: {
diff --git a/gcc/testsuite/rust/compile/issue-2785.rs b/gcc/testsuite/rust/compile/issue-2785.rs
new file mode 100644
index 000000000000..08f6346f60b2
--- /dev/null
+++ b/gcc/testsuite/rust/compile/issue-2785.rs
@@ -0,0 +1,9 @@
+// { dg-additional-options "-frust-edition=2018" }
+trait Foo {
+    async fn foo(){}
+    // { dg-error "functions in traits cannot be declared .async." "" { target *-*-* } .-1 }
+    async fn bar();
+    // { dg-error "functions in traits cannot be declared .async." "" { target *-*-* } .-1 }
+}
+
+fn main() {}