diff --git a/stix2/v20/base.py b/stix2/v20/base.py
index a0d65c6..b5437ca 100644
--- a/stix2/v20/base.py
+++ b/stix2/v20/base.py
@@ -10,10 +10,7 @@ class _STIXBase20(_STIXBase):
 
 
 class _Observable(_Observable, _STIXBase20):
-
-    def __init__(self, **kwargs):
-        self._properties['extensions'].allow_custom = kwargs.get('allow_custom', False)
-        super(_Observable, self).__init__(**kwargs)
+    pass
 
 
 class _Extension(_Extension, _STIXBase20):
diff --git a/stix2/v21/base.py b/stix2/v21/base.py
index 8598a83..90b9fd2 100644
--- a/stix2/v21/base.py
+++ b/stix2/v21/base.py
@@ -6,11 +6,7 @@ from ..base import (
 
 
 class _STIXBase21(_STIXBase):
-
-    def __init__(self, **kwargs):
-        if 'extensions' in self._properties:
-            self._properties['extensions'].allow_custom = kwargs.get('allow_custom', False)
-        super(_STIXBase21, self).__init__(**kwargs)
+    pass
 
 
 class _Observable(_Observable, _STIXBase21):