diff --git a/src/core/IO/Socket/Async.pm6 b/src/core/IO/Socket/Async.pm6
index 133441bd2ef..8345add0d6f 100644
--- a/src/core/IO/Socket/Async.pm6
+++ b/src/core/IO/Socket/Async.pm6
@@ -8,11 +8,13 @@ my class IO::Socket::Async {
     has $!close-promise;
     has $!close-vow;
 
+    subset Port-Number of Int where { !defined($_) or $_ ~~ ^65536 };
+
     has Str $.peer-host;
-    has Int $.peer-port;
+    has Port-Number $.peer-port;
 
     has Str $.socket-host;
-    has Int $.socket-port;
+    has Port-Number $.socket-port;
 
     method new() {
         die "Cannot create an asynchronous socket directly; please use\n" ~
@@ -165,7 +167,7 @@ my class IO::Socket::Async {
         $!close-vow.keep(True);
     }
 
-    method connect(IO::Socket::Async:U: Str() $host, Int() $port,
+    method connect(IO::Socket::Async:U: Str() $host, Int() $port where * ~~ Port-Number,
                    :$enc = 'utf-8', :$scheduler = $*SCHEDULER) {
         my $p = Promise.new;
         my $v = $p.vow;
@@ -290,8 +292,8 @@ my class IO::Socket::Async {
         method serial(--> True) { }
     }
 
-    method listen(IO::Socket::Async:U: Str() $host, Int() $port, Int() $backlog = 128,
-                  :$enc = 'utf-8', :$scheduler = $*SCHEDULER) {
+    method listen(IO::Socket::Async:U: Str() $host, Int() $port where * ~~ Port-Number,
+                  Int() $backlog = 128, :$enc = 'utf-8', :$scheduler = $*SCHEDULER) {
         my $encoding = Encoding::Registry.find($enc);
         Supply.new: SocketListenerTappable.new:
             :$host, :$port, :$backlog, :$encoding, :$scheduler
@@ -329,8 +331,8 @@ my class IO::Socket::Async {
         await $p
     }
 
-    method bind-udp(IO::Socket::Async:U: Str() $host, Int() $port, :$broadcast,
-                    :$enc = 'utf-8', :$scheduler = $*SCHEDULER) {
+    method bind-udp(IO::Socket::Async:U: Str() $host, Int() $port where * ~~ Port-Number,
+                    :$broadcast, :$enc = 'utf-8', :$scheduler = $*SCHEDULER) {
         my $p = Promise.new;
         my $encoding = Encoding::Registry.find($enc);
         nqp::asyncudp(
@@ -355,11 +357,13 @@ my class IO::Socket::Async {
         await $p
     }
 
-    method print-to(IO::Socket::Async:D: Str() $host, Int() $port, Str() $str, :$scheduler = $*SCHEDULER) {
+    method print-to(IO::Socket::Async:D: Str() $host, Int() $port where * ~~ Port-Number,
+                    Str() $str, :$scheduler = $*SCHEDULER) {
         self.write-to($host, $port, $!encoder.encode-chars($str), :$scheduler)
     }
 
-    method write-to(IO::Socket::Async:D: Str() $host, Int() $port, Blob $b, :$scheduler = $*SCHEDULER) {
+    method write-to(IO::Socket::Async:D: Str() $host, Int() $port where * ~~ Port-Number,
+                    Blob $b, :$scheduler = $*SCHEDULER) {
         my $p = Promise.new;
         my $v = $p.vow;
         nqp::asyncwritebytesto(
diff --git a/t/05-messages/02-errors.t b/t/05-messages/02-errors.t
index d277df387c1..37833ef3177 100644
--- a/t/05-messages/02-errors.t
+++ b/t/05-messages/02-errors.t
@@ -16,15 +16,12 @@ throws-like { for [:a] X [:b] -> ($i, $j) { } },
     message => / '<anon>' /,
     "anonymous subs get '<anon>' in arity error messages";
 
-todo 'needs better error message';
-
-skip 'crashes: https://github.com/rakudo/rakudo/issues/2402';
-#throws-like {
-#    sub l { IO::Socket::Async.listen: "localhost", 111390 }
-#    react whenever l() {
-#        whenever l() {} # try to listen on already open sock
-#    }
-#}, X::AdHoc, message => /'something good'/;
+throws-like {
+    sub l { IO::Socket::Async.listen: "localhost", 111390 }
+    react whenever l() {
+        whenever l() {} # try to listen on already open sock
+    }
+}, X::TypeCheck::Binding::Parameter, message => /'type check failed'/;
 
 # RT #132283
 is-deeply class { has $.bar }.^methods».name.sort, <BUILDALL bar>,