diff --git a/NEWS b/NEWS
index d67ab1fa..09b19e5f 100644
--- a/NEWS
+++ b/NEWS
@@ -20,6 +20,7 @@ What's new in psycopg 2.7.5
 - Fixed building on Solaris 11 and derivatives such as SmartOS and illumos
   (:ticket:`#677`).
 - Maybe fixed building on MSYS2 (as reported in :ticket:`#658`).
+- Allow string subclasses in connection and other places (:ticket:`#679`).
 
 
 What's new in psycopg 2.7.4
diff --git a/psycopg/utils.c b/psycopg/utils.c
index a197fe22..261810fd 100644
--- a/psycopg/utils.c
+++ b/psycopg/utils.c
@@ -168,11 +168,11 @@ psycopg_ensure_bytes(PyObject *obj)
     PyObject *rv = NULL;
     if (!obj) { return NULL; }
 
-    if (PyUnicode_CheckExact(obj)) {
+    if (PyUnicode_Check(obj)) {
         rv = PyUnicode_AsUTF8String(obj);
         Py_DECREF(obj);
     }
-    else if (Bytes_CheckExact(obj)) {
+    else if (Bytes_Check(obj)) {
         rv = obj;
     }
     else {
diff --git a/tests/test_connection.py b/tests/test_connection.py
index a82bd499..4625e7e3 100755
--- a/tests/test_connection.py
+++ b/tests/test_connection.py
@@ -246,6 +246,13 @@ class ConnectionTests(ConnectingTestCase):
             else:
                 del os.environ['PGCLIENTENCODING']
 
+    def test_connect_no_string(self):
+        class MyString(str):
+            pass
+
+        conn = psycopg2.connect(MyString(dsn))
+        conn.close()
+
     def test_weakref(self):
         from weakref import ref
         import gc
@@ -400,6 +407,13 @@ class ParseDsnTestCase(ConnectingTestCase):
         self.assertRaises(TypeError, ext.parse_dsn, None)
         self.assertRaises(TypeError, ext.parse_dsn, 42)
 
+    def test_str_subclass(self):
+        class MyString(str):
+            pass
+
+        res = ext.parse_dsn(MyString("dbname=test"))
+        self.assertEqual(res, {'dbname': 'test'})
+
 
 class MakeDsnTestCase(ConnectingTestCase):
     def test_empty_arguments(self):