diff --git a/src/stream_engine.cpp b/src/stream_engine.cpp
index ce2878a2..34ac5c3b 100644
--- a/src/stream_engine.cpp
+++ b/src/stream_engine.cpp
@@ -363,7 +363,6 @@ bool zmq::stream_engine_t::handshake ()
             error ();
             return false;
         }
-
         if (n == 0)
             return false;
 
@@ -390,7 +389,7 @@ bool zmq::stream_engine_t::handshake ()
         if (outpos + outsize != greeting_output_buffer + greeting_size) {
             if (outsize == 0)
                 set_pollout (handle);
-            outpos [outsize++] = 1;             // Protocol revision
+            outpos [outsize++] = ZMTP_2_1;      // Protocol revision
             outpos [outsize++] = options.type;  // Socket type
         }
     }
@@ -432,25 +431,26 @@ bool zmq::stream_engine_t::handshake ()
             decoder->set_msg_sink (this);
     }
     else
-    if (greeting [revision_pos] == 0) {
-        //  ZMTP/1.0 framing (revision 0)
-        encoder = new (std::nothrow) v1_encoder_t (out_batch_size);
+    if (greeting [revision_pos] == ZMTP_1_0) {
+        encoder = new (std::nothrow) v1_encoder_t (
+            out_batch_size);
         alloc_assert (encoder);
         encoder->set_msg_source (session);
 
-        decoder = new (std::nothrow) v1_decoder_t (in_batch_size, options.maxmsgsize);
+        decoder = new (std::nothrow) v1_decoder_t (
+            in_batch_size, options.maxmsgsize);
         alloc_assert (decoder);
         decoder->set_msg_sink (session);
     }
     else
-    if (greeting [revision_pos] == 1
-    ||  greeting [revision_pos] == 2) {
-        //  ZMTP/2.0 framing (revision 1)
-        encoder = new (std::nothrow) v2_encoder_t (out_batch_size, session);
+    if (greeting [revision_pos] == ZMTP_2_0
+    ||  greeting [revision_pos] == ZMTP_2_1) {
+        encoder = new (std::nothrow) v2_encoder_t (
+            out_batch_size, session);
         alloc_assert (encoder);
 
-        decoder = new (std::nothrow)
-            v2_decoder_t (in_batch_size, options.maxmsgsize, session);
+        decoder = new (std::nothrow) v2_decoder_t (
+            in_batch_size, options.maxmsgsize, session);
         alloc_assert (decoder);
     }
 
diff --git a/src/stream_engine.hpp b/src/stream_engine.hpp
index 80cceaab..0bbbcade 100644
--- a/src/stream_engine.hpp
+++ b/src/stream_engine.hpp
@@ -34,6 +34,13 @@
 
 namespace zmq
 {
+    //  Protocol revisions
+    enum
+    {
+        ZMTP_1_0 = 0,
+        ZMTP_2_0 = 1,
+        ZMTP_2_1 = 2
+    };
 
     class io_thread_t;
     class session_base_t;
diff --git a/src/v2_protocol.hpp b/src/v2_protocol.hpp
index 805f5d14..2e26add1 100644
--- a/src/v2_protocol.hpp
+++ b/src/v2_protocol.hpp
@@ -36,4 +36,3 @@ namespace zmq
 }
 
 #endif
-
diff --git a/tests/test_raw_sock.cpp b/tests/test_raw_sock.cpp
index e3bfdcda..de4c6ead 100644
--- a/tests/test_raw_sock.cpp
+++ b/tests/test_raw_sock.cpp
@@ -29,7 +29,7 @@
 typedef unsigned char byte;
 typedef struct {
     byte signature [10];    //  0xFF 8*0x00 0x7F
-    byte revision;          //  0x01 = ZMTP/2.0
+    byte revision;          //  2 = ZMTP/2.1
     byte socktype;          //  Defined in ZMTP spec
     byte identity [2];      //  Empty message
 } zmtp_greeting_t;
@@ -41,7 +41,7 @@ typedef struct {
 //  8-byte size is set to 1 for backwards compatibility
 
 static zmtp_greeting_t greeting
-    = { { 0xFF, 0, 0, 0, 0, 0, 0, 0, 1, 0x7F }, 1, 0, { 0, 0 } };
+    = { { 0xFF, 0, 0, 0, 0, 0, 0, 0, 1, 0x7F }, 2, 0, { 0, 0 } };
 
 int main (void)
 {
@@ -107,7 +107,7 @@ int main (void)
     assert (rc == 11);
 
     //  First four bytes are [revision][socktype][identity]
-    assert (buffer [0] == 1);
+    assert (buffer [0] == 2);       //  ZMTP/2.1
     assert (buffer [1] == ZMTP_DEALER);
 
     //  Identity is 2 byte message