diff --git a/psycopg/cursor_type.c b/psycopg/cursor_type.c
index b06371a..e7d7fde 100644
--- a/psycopg/cursor_type.c
+++ b/psycopg/cursor_type.c
@@ -174,6 +174,11 @@ _mogrify(PyObject *var, PyObject *fmt, cursorObject *curs, PyObject **new)
                        if it was added to the dictionary directly; good */
                     Py_XDECREF(value);
                 }
+                else {
+                  /* well, we found the value in 'n' but we've already
+                     called PyObject_GetItem, so we have to decrement */
+		  Py_XDECREF(value);
+                }
                 Py_DECREF(key); /* key has the original refcnt now */
                 Dprintf("_mogrify: after value refcnt: "
                     FORMAT_CODE_PY_SSIZE_T, Py_REFCNT(value));