diff --git a/cyclonedx/model/__init__.py b/cyclonedx/model/__init__.py
index 2c62ac56..282cdd91 100644
--- a/cyclonedx/model/__init__.py
+++ b/cyclonedx/model/__init__.py
@@ -150,11 +150,14 @@ class ExternalReference:
     _hashes: List[HashType] = []
 
     def __init__(self, reference_type: ExternalReferenceType, url: str, comment: str = None,
-                 hashes: List[HashType] = []):
+                 hashes: List[HashType] = None):
         self._reference_type = reference_type
         self._url = url
         self._comment = comment
-        self._hashes = hashes
+        if not hashes:
+            self._hashes.clear()
+        else:
+            self._hashes = hashes
 
     def add_hash(self, our_hash: HashType):
         """
diff --git a/tests/test_parser_pipenv.py b/tests/test_parser_pipenv.py
index be139718..fb4904c3 100644
--- a/tests/test_parser_pipenv.py
+++ b/tests/test_parser_pipenv.py
@@ -34,3 +34,4 @@ def test_simple(self):
         self.assertEqual('toml', components[0].get_name())
         self.assertEqual('0.10.2', components[0].get_version())
         self.assertEqual(len(components[0].get_external_references()), 2)
+        self.assertEqual(len(components[0].get_external_references()[0].get_hashes()), 1)