diff --git a/ChangeLog b/ChangeLog
index cc318ff2..244710cc 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+2010-11-16  Daniele Varrazzo  <daniele.varrazzo@gmail.com>
+
+	* psycopg/connection_int.c: abort connection to protocol 2 server.
+
 2010-11-11  Daniele Varrazzo  <daniele.varrazzo@gmail.com>
 
 	* lib/extras.py: build the namedtuple only once per execution, not once
diff --git a/NEWS-2.3 b/NEWS-2.3
index 87f03ca1..bf1e628b 100644
--- a/NEWS-2.3
+++ b/NEWS-2.3
@@ -13,6 +13,8 @@ psycopg 2.3 aims to expose some new features introduced in PostgreSQL 9.0.
 
 * Other features and changes:
 
+  - Dropped support for protocol 2: Psycopg 2.3 can only connect to PostgreSQL
+    servers with version at least 7.4.
   - `mogrify()` now supports unicode queries.
   - subclasses of a type that can be adapted are adapted as the superclass.
   - `errorcodes` knows a couple of new codes introduced in PostgreSQL 9.0.
diff --git a/doc/src/connection.rst b/doc/src/connection.rst
index 624fcba7..22241fed 100644
--- a/doc/src/connection.rst
+++ b/doc/src/connection.rst
@@ -428,7 +428,9 @@ The ``connection`` class
     .. attribute:: protocol_version
 
         A read-only integer representing frontend/backend protocol being used.
-        It can be 2 or 3.
+        Currently Psycopg supports only protocol 3, which allows connection
+        to PostgreSQL server from version 7.4. Psycopg versions previous than
+        2.3 support both protocols 2 and 3.
 
         .. seealso:: libpq docs for `PQprotocolVersion()`__ for details.
 
diff --git a/psycopg/connection_int.c b/psycopg/connection_int.c
index 7f864608..e335c396 100644
--- a/psycopg/connection_int.c
+++ b/psycopg/connection_int.c
@@ -295,6 +295,10 @@ conn_setup(connectionObject *self, PGconn *pgconn)
     self->equote = conn_get_standard_conforming_strings(pgconn);
     self->server_version = conn_get_server_version(pgconn);
     self->protocol = conn_get_protocol_version(self->pgconn);
+    if (3 != self->protocol) {
+        PyErr_SetString(InterfaceError, "only protocol 3 supported");
+        return -1;
+    }
 
     Py_BEGIN_ALLOW_THREADS;
     pthread_mutex_lock(&self->lock);
@@ -636,6 +640,10 @@ _conn_poll_setup_async(connectionObject *self)
         self->equote = conn_get_standard_conforming_strings(self->pgconn);
         self->protocol = conn_get_protocol_version(self->pgconn);
         self->server_version = conn_get_server_version(self->pgconn);
+        if (3 != self->protocol) {
+            PyErr_SetString(InterfaceError, "only protocol 3 supported");
+            break;
+        }
 
         /* asynchronous connections always use isolation level 0, the user is
          * expected to manage the transactions himself, by sending