diff --git a/psycopg/adapter_binary.c b/psycopg/adapter_binary.c
index 2574c603..da3bec60 100644
--- a/psycopg/adapter_binary.c
+++ b/psycopg/adapter_binary.c
@@ -149,16 +149,14 @@ binary_str(binaryObject *self)
 static PyObject *
 binary_prepare(binaryObject *self, PyObject *args)
 {
-    connectionObject *conn;
+    PyObject *conn;
 
-    if (!PyArg_ParseTuple(args, "O", &conn))
+    if (!PyArg_ParseTuple(args, "O!", &connectionType, &conn))
         return NULL;
 
     Py_XDECREF(self->conn);
-    if (conn) {
-        self->conn = (PyObject*)conn;
-        Py_INCREF(self->conn);
-    }
+    self->conn = conn;
+    Py_INCREF(self->conn);
 
     Py_INCREF(Py_None);
     return Py_None;
diff --git a/psycopg/adapter_list.c b/psycopg/adapter_list.c
index cbb75422..d97ecfb1 100644
--- a/psycopg/adapter_list.c
+++ b/psycopg/adapter_list.c
@@ -98,9 +98,9 @@ list_getquoted(listObject *self, PyObject *args)
 static PyObject *
 list_prepare(listObject *self, PyObject *args)
 {
-    connectionObject *conn;
+    PyObject *conn;
 
-    if (!PyArg_ParseTuple(args, "O", &conn))
+    if (!PyArg_ParseTuple(args, "O!", &connectionType, &conn))
         return NULL;
 
     /* note that we don't copy the encoding from the connection, but take a
@@ -109,7 +109,7 @@ list_prepare(listObject *self, PyObject *args)
        work even without a connection to the backend. */
     Py_CLEAR(self->connection);
     Py_INCREF(conn);
-    self->connection = (PyObject*)conn;
+    self->connection = conn;
 
     Py_INCREF(Py_None);
     return Py_None;
diff --git a/psycopg/adapter_qstring.c b/psycopg/adapter_qstring.c
index 4240d382..773cfa0d 100644
--- a/psycopg/adapter_qstring.c
+++ b/psycopg/adapter_qstring.c
@@ -124,24 +124,22 @@ qstring_str(qstringObject *self)
 static PyObject *
 qstring_prepare(qstringObject *self, PyObject *args)
 {
-    connectionObject *conn;
+    PyObject *conn;
 
-    if (!PyArg_ParseTuple(args, "O", &conn))
+    if (!PyArg_ParseTuple(args, "O!", &connectionType, &conn))
         return NULL;
 
     /* we bother copying the encoding only if the wrapped string is unicode,
        we don't need the encoding if that's not the case */
     if (PyUnicode_Check(self->wrapped)) {
         if (self->encoding) free(self->encoding);
-        self->encoding = strdup(conn->codec);
-        Dprintf("qstring_prepare: set encoding to %s", conn->codec);
+        self->encoding = strdup(((connectionObject *)conn)->codec);
+        Dprintf("qstring_prepare: set encoding to %s", self->encoding);
     }
 
     Py_CLEAR(self->conn);
-    if (conn) {
-        Py_INCREF(conn);
-        self->conn = (PyObject*)conn;
-    }
+    Py_INCREF(conn);
+    self->conn = conn;
 
     Py_INCREF(Py_None);
     return Py_None;