diff --git a/src/pkg/net/sock_posix.go b/src/pkg/net/sock_posix.go
index c8a94f5047..e2487c805e 100644
--- a/src/pkg/net/sock_posix.go
+++ b/src/pkg/net/sock_posix.go
@@ -25,7 +25,8 @@ func socket(net string, f, t, p int, ipv6only bool, ulsa, ursa syscall.Sockaddr,
 		return nil, err
 	}
 
-	if ulsa != nil {
+	// This socket is used by a listener.
+	if ulsa != nil && ursa == nil {
 		// We provide a socket that listens to a wildcard
 		// address with reusable UDP port when the given ulsa
 		// is an appropriate UDP multicast address prefix.
@@ -37,6 +38,9 @@ func socket(net string, f, t, p int, ipv6only bool, ulsa, ursa syscall.Sockaddr,
 			closesocket(s)
 			return nil, err
 		}
+	}
+
+	if ulsa != nil {
 		if err = syscall.Bind(s, ulsa); err != nil {
 			closesocket(s)
 			return nil, err
@@ -48,6 +52,7 @@ func socket(net string, f, t, p int, ipv6only bool, ulsa, ursa syscall.Sockaddr,
 		return nil, err
 	}
 
+	// This socket is used by a dialer.
 	if ursa != nil {
 		if !deadline.IsZero() {
 			setWriteDeadline(fd, deadline)