diff --git a/test/socket/test_unix.rb b/test/socket/test_unix.rb
index d8cf7139e9..bde17cf0ab 100644
--- a/test/socket/test_unix.rb
+++ b/test/socket/test_unix.rb
@@ -168,6 +168,7 @@ class TestSocket_UNIXSocket < Test::Unit::TestCase
 
   def test_recvmsg
     return if !defined?(Socket::SCM_RIGHTS)
+    return if !defined?(Socket::AncillaryData)
     IO.pipe {|r1, w|
       UNIXSocket.pair {|s1, s2|
         s1.send_io(r1)