diff --git a/ChangeLog b/ChangeLog
index f5d1b5a2e3..48e4ed11f6 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,11 @@
+Tue Nov 17 14:04:14 2015  NAKAMURA Usaku  <usa@ruby-lang.org>
+
+	* ext/socket/lib/socket.rb (Socket#recvmsg{,_nonblock}): default values
+	  of clen must be nil.
+
+	* ext/socket/ancdata.c (bsock_sendmsg_internal): handle nil of clen.
+	  fixes test errors introduced at r52602.
+
 Tue Nov 17 13:43:46 2015  NAKAMURA Usaku  <usa@ruby-lang.org>
 
 	* ext/socket/lib/socket.rb: UNIXSocket is not always exists.  fixes
diff --git a/ext/socket/ancdata.c b/ext/socket/ancdata.c
index 7e0441c042..168f70c311 100644
--- a/ext/socket/ancdata.c
+++ b/ext/socket/ancdata.c
@@ -1467,7 +1467,7 @@ bsock_recvmsg_internal(VALUE sock,
 
     maxdatlen = NUM2SIZET(vmaxdatlen);
 #if defined(HAVE_STRUCT_MSGHDR_MSG_CONTROL)
-    maxctllen = NUM2SIZET(vmaxctllen);
+    maxctllen = NIL_P(vmaxctllen) ? 4096 : NUM2SIZET(vmaxctllen);
 #else
     if (!NIL_P(vmaxctllen))
         rb_raise(rb_eArgError, "control message not supported");
diff --git a/ext/socket/lib/socket.rb b/ext/socket/lib/socket.rb
index df526d73c6..58e7dfd92a 100644
--- a/ext/socket/lib/socket.rb
+++ b/ext/socket/lib/socket.rb
@@ -425,7 +425,7 @@ class BasicSocket < IO
   #       return ancdata.unix_rights[0]
   #     end
   #   }
-  def recvmsg(dlen = 4096, flags = 0, clen = 4096, scm_rights: false)
+  def recvmsg(dlen = 4096, flags = 0, clen = nil, scm_rights: false)
     __recvmsg(dlen, flags, clen, scm_rights)
   end
 
@@ -441,7 +441,7 @@ class BasicSocket < IO
   # By specifying `exception: false`, the _opts_ hash allows you to indicate
   # that recvmsg_nonblock should not raise an IO::WaitWritable exception, but
   # return the symbol :wait_writable instead.
-  def recvmsg_nonblock(dlen = 4096, flags = 0, clen = 4096,
+  def recvmsg_nonblock(dlen = 4096, flags = 0, clen = nil,
                        scm_rights: false, exception: true)
     __recvmsg_nonblock(dlen, flags, clen, scm_rights, exception)
   end