diff --git a/NEWS b/NEWS
index ff9d0eb1..1c439323 100644
--- a/NEWS
+++ b/NEWS
@@ -1,6 +1,8 @@
 What's new in psycopg 2.4.2
 ---------------------------
 
+  - Allow using the isolation level "repeatable read" which is distinct
+    from "serializable" in PostgreSQL 9.1.
   - Don't build mx.DateTime support if the module can't be imported
     (ticket #53).
 
diff --git a/lib/extensions.py b/lib/extensions.py
index 82e17fa4..cb48b793 100644
--- a/lib/extensions.py
+++ b/lib/extensions.py
@@ -68,13 +68,11 @@ except ImportError:
     pass
 
 """Isolation level values."""
-ISOLATION_LEVEL_AUTOCOMMIT     = 0
-ISOLATION_LEVEL_READ_COMMITTED = 1 
-ISOLATION_LEVEL_SERIALIZABLE   = 2
-
-# PostgreSQL maps the the other standard values to already defined levels
-ISOLATION_LEVEL_REPEATABLE_READ  = ISOLATION_LEVEL_SERIALIZABLE
-ISOLATION_LEVEL_READ_UNCOMMITTED = ISOLATION_LEVEL_READ_COMMITTED
+ISOLATION_LEVEL_AUTOCOMMIT          = 0
+ISOLATION_LEVEL_READ_UNCOMMITTED    = 1
+ISOLATION_LEVEL_READ_COMMITTED      = 2
+ISOLATION_LEVEL_REPEATABLE_READ     = 3
+ISOLATION_LEVEL_SERIALIZABLE        = 4
 
 """psycopg connection status values."""
 STATUS_SETUP    = 0
diff --git a/psycopg/connection.h b/psycopg/connection.h
index 552b93d7..262e6ac2 100644
--- a/psycopg/connection.h
+++ b/psycopg/connection.h
@@ -63,9 +63,11 @@ extern "C" {
 
 /* possible values for isolation_level */
 typedef enum {
-    ISOLATION_LEVEL_AUTOCOMMIT      = 0,
-    ISOLATION_LEVEL_READ_COMMITTED  = 1,
-    ISOLATION_LEVEL_SERIALIZABLE    = 2,
+    ISOLATION_LEVEL_AUTOCOMMIT          = 0,
+    ISOLATION_LEVEL_READ_UNCOMMITTED    = 1,
+    ISOLATION_LEVEL_READ_COMMITTED      = 2,
+    ISOLATION_LEVEL_REPEATABLE_READ     = 3,
+    ISOLATION_LEVEL_SERIALIZABLE        = 4,
 } conn_isolation_level_t;
 
 extern HIDDEN PyTypeObject connectionType;
diff --git a/psycopg/connection_type.c b/psycopg/connection_type.c
index 7ca395dc..2d02b86b 100644
--- a/psycopg/connection_type.c
+++ b/psycopg/connection_type.c
@@ -400,9 +400,9 @@ psyco_conn_set_isolation_level(connectionObject *self, PyObject *args)
 
     if (!PyArg_ParseTuple(args, "i", &level)) return NULL;
 
-    if (level < 0 || level > 2) {
+    if (level < 0 || level > 4) {
         PyErr_SetString(PyExc_ValueError,
-            "isolation level must be between 0 and 2");
+            "isolation level must be between 0 and 4");
         return NULL;
     }
 
diff --git a/psycopg/pqpath.c b/psycopg/pqpath.c
index 6a6d05a3..a6144229 100644
--- a/psycopg/pqpath.c
+++ b/psycopg/pqpath.c
@@ -408,7 +408,9 @@ pq_begin_locked(connectionObject *conn, PGresult **pgres, char **error,
 {
     const char *query[] = {
         NULL,
+        "BEGIN; SET TRANSACTION ISOLATION LEVEL READ UNCOMMITTED",
         "BEGIN; SET TRANSACTION ISOLATION LEVEL READ COMMITTED",
+        "BEGIN; SET TRANSACTION ISOLATION LEVEL REPEATABLE READ",
         "BEGIN; SET TRANSACTION ISOLATION LEVEL SERIALIZABLE"};
     int result;
 
diff --git a/tests/test_connection.py b/tests/test_connection.py
index d9da471f..89b104f4 100755
--- a/tests/test_connection.py
+++ b/tests/test_connection.py
@@ -201,24 +201,30 @@ class IsolationLevelsTestCase(unittest.TestCase):
 
     def test_set_isolation_level(self):
         conn = self.connect()
+        curs = conn.cursor()
 
-        conn.set_isolation_level(
-            psycopg2.extensions.ISOLATION_LEVEL_AUTOCOMMIT)
-        self.assertEqual(conn.isolation_level,
-            psycopg2.extensions.ISOLATION_LEVEL_AUTOCOMMIT)
+        for name, level in (
+            (None, psycopg2.extensions.ISOLATION_LEVEL_AUTOCOMMIT),
+            ('read uncommitted', psycopg2.extensions.ISOLATION_LEVEL_READ_UNCOMMITTED),
+            ('read committed', psycopg2.extensions.ISOLATION_LEVEL_READ_COMMITTED),
+            ('repeatable read', psycopg2.extensions.ISOLATION_LEVEL_REPEATABLE_READ),
+            ('serializable', psycopg2.extensions.ISOLATION_LEVEL_SERIALIZABLE),
+        ):
+            conn.set_isolation_level(level)
+            self.assertEqual(conn.isolation_level, level)
 
-        conn.set_isolation_level(
-            psycopg2.extensions.ISOLATION_LEVEL_READ_COMMITTED)
-        self.assertEqual(conn.isolation_level,
-            psycopg2.extensions.ISOLATION_LEVEL_READ_COMMITTED)
+            curs.execute('show transaction_isolation;')
+            got_name = curs.fetchone()[0]
 
-        conn.set_isolation_level(
-            psycopg2.extensions.ISOLATION_LEVEL_SERIALIZABLE)
-        self.assertEqual(conn.isolation_level,
-            psycopg2.extensions.ISOLATION_LEVEL_SERIALIZABLE)
+            if name is None:
+                curs.execute('show default_transaction_isolation;')
+                name = curs.fetchone()[0]
+
+            self.assertEqual(name, got_name)
+            conn.commit()
 
         self.assertRaises(ValueError, conn.set_isolation_level, -1)
-        self.assertRaises(ValueError, conn.set_isolation_level, 3)
+        self.assertRaises(ValueError, conn.set_isolation_level, 5)
 
     def test_set_isolation_level_abort(self):
         conn = self.connect()