diff --git a/NEWS b/NEWS
index c3270f00..b97a7ee5 100644
--- a/NEWS
+++ b/NEWS
@@ -1,3 +1,16 @@
+0MQ version 4.0.1 (RC2), released on 2013/
+===============================================
+
+Bug fixes
+---------
+
+* Fixed some build/test errors on OS/X + Clang++.
+
+* Updated CURVE mechanism to track revised RFC 27 (INITIATE vouch).
+
+* Fixed LIBZMQ-566 (dealer-to-router connections sometimes failing).
+
+
 0MQ version 4.0.0 (RC1), released on 2013/09/20
 ===============================================
 
diff --git a/include/zmq.h b/include/zmq.h
index bf997973..ee529c2f 100644
--- a/include/zmq.h
+++ b/include/zmq.h
@@ -77,7 +77,7 @@ typedef unsigned __int8 uint8_t;
 /*  Version macros for compile-time API version detection                     */
 #define ZMQ_VERSION_MAJOR 4
 #define ZMQ_VERSION_MINOR 0
-#define ZMQ_VERSION_PATCH 0
+#define ZMQ_VERSION_PATCH 1
 
 #define ZMQ_MAKE_VERSION(major, minor, patch) \
     ((major) * 10000 + (minor) * 100 + (patch))
diff --git a/src/options.cpp b/src/options.cpp
index 84f36a7f..ea932b03 100644
--- a/src/options.cpp
+++ b/src/options.cpp
@@ -286,7 +286,7 @@ int zmq::options_t::setsockopt (int option_, const void *optval_,
             break;
 
         case ZMQ_ZAP_DOMAIN:
-            if (optvallen_ >= 0 && optvallen_ < 256) {
+            if (optvallen_ < 256) {
                 zap_domain.assign ((const char *) optval_, optvallen_);
                 return 0;
             }
diff --git a/src/stream_engine.cpp b/src/stream_engine.cpp
index 88ff499d..9b053c83 100644
--- a/src/stream_engine.cpp
+++ b/src/stream_engine.cpp
@@ -652,6 +652,7 @@ void zmq::stream_engine_t::mechanism_ready ()
             return;
         }
         errno_assert (rc == 0);
+        session->flush ();
     }
 
     read_msg = &stream_engine_t::pull_and_encode;
diff --git a/tests/test_stream.cpp b/tests/test_stream.cpp
index 2eaac50c..3e9a34e9 100644
--- a/tests/test_stream.cpp
+++ b/tests/test_stream.cpp
@@ -102,7 +102,6 @@ test_stream_to_dealer (void)
         assert (rc >= 0);
         bytes_read += rc;
     }
-    assert (rc == 97);
 
     //  First two bytes are major and minor version numbers.
     assert (buffer [0] == 3);       //  ZMTP/3.0
diff --git a/tools/curve_keygen.c b/tools/curve_keygen.c
index 7a5da02e..c18c4621 100644
--- a/tools/curve_keygen.c
+++ b/tools/curve_keygen.c
@@ -24,6 +24,7 @@
     along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
 
+#include <assert.h>
 #include <zmq_utils.h>
 #ifdef HAVE_LIBSODIUM
 #   include <sodium.h>