diff --git a/google/oauth2/credentials.py b/google/oauth2/credentials.py
index a2d41bd3a..7e2173ebe 100644
--- a/google/oauth2/credentials.py
+++ b/google/oauth2/credentials.py
@@ -148,7 +148,7 @@ def __init__(
         self.refresh_handler = refresh_handler
         self._enable_reauth_refresh = enable_reauth_refresh
         self._trust_boundary = trust_boundary
-        self._universe_domain = universe_domain
+        self._universe_domain = universe_domain or _DEFAULT_UNIVERSE_DOMAIN
 
     def __getstate__(self):
         """A __getstate__ method must exist for the __setstate__ to be called
diff --git a/google/oauth2/service_account.py b/google/oauth2/service_account.py
index 4b99e16eb..68db41af4 100644
--- a/google/oauth2/service_account.py
+++ b/google/oauth2/service_account.py
@@ -182,10 +182,7 @@ def __init__(
         self._quota_project_id = quota_project_id
         self._token_uri = token_uri
         self._always_use_jwt_access = always_use_jwt_access
-        if not universe_domain:
-            self._universe_domain = _DEFAULT_UNIVERSE_DOMAIN
-        else:
-            self._universe_domain = universe_domain
+        self._universe_domain = universe_domain or _DEFAULT_UNIVERSE_DOMAIN
 
         if universe_domain != _DEFAULT_UNIVERSE_DOMAIN:
             self._always_use_jwt_access = True