diff --git a/misp_stix_converter/stix2misp/external_stix1_to_misp.py b/misp_stix_converter/stix2misp/external_stix1_to_misp.py
index e848ab7..7cf9ae1 100644
--- a/misp_stix_converter/stix2misp/external_stix1_to_misp.py
+++ b/misp_stix_converter/stix2misp/external_stix1_to_misp.py
@@ -14,7 +14,7 @@
 from stix.indicator import Indicator
 from stix.threat_actor import ThreatActor
 from stix.ttp import TTP
-from typing import Optional
+from typing import Optional, Union
 
 class ExternalSTIX1toMISPParser(STIX1toMISPParser, ExternalSTIXtoMISPParser):
     def __init__(self):
@@ -165,7 +165,7 @@ def _parse_attributes_from_ttp(self, ttp: TTP, galaxies: set):
             attributes[0].update(self._sanitise_attribute_uuid(ttp.id_))
         return attributes
 
-    def _parse_description(self, stix_object: Indicator | Observable):
+    def _parse_description(self, stix_object: Union[Indicator, Observable]):
         if stix_object.description:
             misp_attribute = {
                 'type': 'text', 'value': stix_object.description.value