diff --git a/scripts/Python/python-wrapper.swig b/scripts/Python/python-wrapper.swig
index d68c1b9..787074e 100644
--- a/scripts/Python/python-wrapper.swig
+++ b/scripts/Python/python-wrapper.swig
@@ -645,9 +645,11 @@
                         err_msg.clear();
                         retval = true;
                     }
-                    else // return value is an error string
+                    else
                     {
-                        err_msg.assign(PyString_AsString(pvalue));
+                        // return value is an error string
+                        if (PyString_CheckExact(pvalue))
+                            err_msg.assign(PyString_AsString(pvalue));
                         retval = false;
                     }
                     Py_DECREF (pvalue);