diff --git a/NEWS b/NEWS
index 3753462c..2f3b8650 100644
--- a/NEWS
+++ b/NEWS
@@ -13,6 +13,8 @@ What's new in psycopg 2.4.6
     Thanks to Manu Cupcic for the report (ticket #110).
   - 'register_hstore()', 'register_composite()', 'tpc_recover()' work with
     RealDictConnection and Cursor (ticket #114).
+  - connect() raises an exception instead of swallowing keyword arguments
+    when a connection string is specified as well (ticket #131).
   - 'errorcodes' map updated to PostgreSQL 9.2.
 
 
diff --git a/lib/__init__.py b/lib/__init__.py
index 0a8ed0f5..892d8038 100644
--- a/lib/__init__.py
+++ b/lib/__init__.py
@@ -146,37 +146,36 @@ def connect(dsn=None,
     Using *async*=True an asynchronous connection will be created.
 
     Any other keyword parameter will be passed to the underlying client
-    library: the list of supported parameter depends on the library version.
+    library: the list of supported parameters depends on the library version.
 
     """
+    items = []
+    if database is not None:
+        items.append(('dbname', database))
+    if user is not None:
+        items.append(('user', user))
+    if password is not None:
+        items.append(('password', password))
+    if host is not None:
+        items.append(('host', host))
+    if port is not None:
+        items.append(('port', port))
+
+    items.extend([(k, v) for (k, v) in kwargs.iteritems() if v is not None])
+
+    if dsn is not None and items:
+        raise TypeError(
+            "'%s' is an invalid keyword argument when the dsn is specified"
+                % items[0][0])
+
     if dsn is None:
-        # Note: reproducing the behaviour of the previous C implementation:
-        # keyword are silently swallowed if a DSN is specified. I would have
-        # raised an exception. File under "histerical raisins".
-        items = []
-        if database is not None:
-            items.append(('dbname', database))
-        if user is not None:
-            items.append(('user', user))
-        if password is not None:
-            items.append(('password', password))
-        if host is not None:
-            items.append(('host', host))
-        # Reproducing the previous C implementation behaviour: swallow a
-        # negative port. The libpq would raise an exception for it.
-        if port is not None and int(port) > 0:
-            items.append(('port', port))
+        if not items:
+            raise TypeError('missing dsn and no parameters')
+        else:
+            dsn = " ".join(["%s=%s" % (k, _param_escape(str(v)))
+                for (k, v) in items])
 
-        items.extend(
-            [(k, v) for (k, v) in kwargs.iteritems() if v is not None])
-        dsn = " ".join(["%s=%s" % (k, _param_escape(str(v)))
-            for (k, v) in items])
-
-        if not dsn:
-            raise InterfaceError('missing dsn and no parameters')
-
-    return _connect(dsn,
-        connection_factory=connection_factory, async=async)
+    return _connect(dsn, connection_factory=connection_factory, async=async)
 
 
 __all__ = filter(lambda k: not k.startswith('_'), locals().keys())
diff --git a/tests/test_module.py b/tests/test_module.py
index 870dbbc2..4083c368 100755
--- a/tests/test_module.py
+++ b/tests/test_module.py
@@ -40,10 +40,10 @@ class ConnectTestCase(unittest.TestCase):
         psycopg2._connect = self._connect_orig
 
     def test_there_has_to_be_something(self):
-        self.assertRaises(psycopg2.InterfaceError, psycopg2.connect)
-        self.assertRaises(psycopg2.InterfaceError, psycopg2.connect,
+        self.assertRaises(TypeError, psycopg2.connect)
+        self.assertRaises(TypeError, psycopg2.connect,
             connection_factory=lambda dsn, async=False: None)
-        self.assertRaises(psycopg2.InterfaceError, psycopg2.connect,
+        self.assertRaises(TypeError, psycopg2.connect,
             async=True)
 
     def test_no_keywords(self):
@@ -127,6 +127,14 @@ class ConnectTestCase(unittest.TestCase):
         psycopg2.connect(database=r"\every thing'")
         self.assertEqual(self.args[0], r"dbname='\\every thing\''")
 
+    def test_no_kwargs_swallow(self):
+        self.assertRaises(TypeError,
+            psycopg2.connect, 'dbname=foo', database='foo')
+        self.assertRaises(TypeError,
+            psycopg2.connect, 'dbname=foo', user='postgres')
+        self.assertRaises(TypeError,
+            psycopg2.connect, 'dbname=foo', no_such_param='meh')
+
 
 class ExceptionsTestCase(unittest.TestCase):
     def setUp(self):