diff --git a/synapse/api/errors.py b/synapse/api/errors.py
index b400149023..caab6c4d6d 100644
--- a/synapse/api/errors.py
+++ b/synapse/api/errors.py
@@ -525,7 +525,7 @@ class MSC4335UserLimitExceededError(SynapseError):
         code: int,
         msg: str,
         info_uri: str,
-        soft_limit: bool,
+        soft_limit: bool = False,
         increase_uri: Optional[str] = None,
     ):
         if soft_limit and increase_uri is None:
@@ -533,8 +533,11 @@ class MSC4335UserLimitExceededError(SynapseError):
 
         additional_fields: dict[str, Union[str, bool]] = {
             "org.matrix.msc4335.info_uri": info_uri,
-            "org.matrix.msc4335.soft_limit": soft_limit,
         }
+
+        if soft_limit:
+            additional_fields["org.matrix.msc4335.soft_limit"] = soft_limit
+
         if soft_limit and increase_uri is not None:
             additional_fields["org.matrix.msc4335.increase_uri"] = increase_uri
 
diff --git a/tests/rest/client/test_media.py b/tests/rest/client/test_media.py
index d5c2654849..51d03daeff 100644
--- a/tests/rest/client/test_media.py
+++ b/tests/rest/client/test_media.py
@@ -3087,7 +3087,7 @@ class MediaUploadLimits(unittest.HomeserverTestCase):
         self.assertEqual(
             channel.json_body["org.matrix.msc4335.info_uri"], "https://example.com"
         )
-        self.assertEqual(channel.json_body["org.matrix.msc4335.soft_limit"], False)
+        self.assertEquals(hasattr(channel.json_body, "org.matrix.msc4335.increase_uri"), False)
 
     @override_config(
         {