diff --git a/NEWS b/NEWS
index 90477661..3f7b6088 100644
--- a/NEWS
+++ b/NEWS
@@ -18,6 +18,7 @@ New features:
   structure (:ticket:`#782`).
 - `~psycopg2.sql.Identifier` can represent qualified names in SQL composition
   (:ticket:`#732`).
+- Fixed adaptation of numeric subclasses such as `IntEnum` (:ticket:`591`).
 - `!str()` on `~psycopg2.extras.Range` produces a human-readable representation
   (:ticket:`#773`).
 - `~psycopg2.extras.DictCursor` and `~psycopg2.extras.RealDictCursor` rows
diff --git a/psycopg/adapter_pint.c b/psycopg/adapter_pint.c
index 18c74b28..72bbdbfe 100644
--- a/psycopg/adapter_pint.c
+++ b/psycopg/adapter_pint.c
@@ -35,8 +35,27 @@
 static PyObject *
 pint_getquoted(pintObject *self, PyObject *args)
 {
-    PyObject *res;
-    if (!(res = PyObject_Str(self->wrapped))) {
+    PyObject *res = NULL;
+
+    /* Convert subclass to int to handle IntEnum and other subclasses
+     * whose str() is not the number. */
+    if (PyLong_CheckExact(self->wrapped)
+#if PY_MAJOR_VERSION < 2
+        || PyInt_CheckExact(self->wrapped)
+#endif
+       ) {
+        res = PyObject_Str(self->wrapped);
+    } else {
+        PyObject *tmp;
+        if (!(tmp = PyObject_CallFunctionObjArgs(
+                (PyObject *)&PyLong_Type, self->wrapped, NULL))) {
+            goto exit;
+        }
+        res = PyObject_Str(tmp);
+        Py_DECREF(tmp);
+    }
+
+    if (!res) {
         goto exit;
     }
 
diff --git a/tests/test_types_basic.py b/tests/test_types_basic.py
index 499fdd18..626ac744 100755
--- a/tests/test_types_basic.py
+++ b/tests/test_types_basic.py
@@ -382,6 +382,18 @@ class TypesBasicTests(ConnectingTestCase):
         a = self.execute("select '{10:20:30:40:50:60}'::macaddr[]")
         self.assertEqual(a, ['10:20:30:40:50:60'])
 
+    @testutils.skip_before_python(3, 4)
+    def testIntEnum(self):
+        from enum import IntEnum
+
+        class Color(IntEnum):
+            RED = 1
+            GREEN = 2
+            BLUE = 4
+
+        a = self.execute("select %s", (Color.GREEN,))
+        self.assertEqual(a, Color.GREEN)
+
 
 class AdaptSubclassTest(unittest.TestCase):
     def test_adapt_subtype(self):