diff --git a/src/core/asyncops.pm b/src/core/asyncops.pm
index 50df8ea8266..e517f5b2f1e 100644
--- a/src/core/asyncops.pm
+++ b/src/core/asyncops.pm
@@ -7,7 +7,10 @@ proto sub await(|) { * }
 multi sub await() {
     die "Must specify a Promise or Channel to await on (got an empty list)";
 }
-multi sub await(Any $x) {
+multi sub await(Any:U $x) {
+    die "Must specify a defined Promise or Channel to await on (got an undefined $x.^name())";
+}
+multi sub await(Any:D $x) {
     die "Must specify a Promise or Channel to await on (got a $x.^name())";
 }
 multi sub await(Iterable:D $i) { $i.eager.map({ await $_ }) }