diff --git a/proto/message.py b/proto/message.py
index 08e6623f..28a87a80 100644
--- a/proto/message.py
+++ b/proto/message.py
@@ -327,7 +327,13 @@ def deserialize(cls, payload: bytes) -> "Message":
         """
         return cls.wrap(cls.pb().FromString(payload))
 
-    def to_json(cls, instance, *, use_integers_for_enums=True) -> str:
+    def to_json(
+        cls,
+        instance,
+        *,
+        use_integers_for_enums=True,
+        including_default_value_fields=True
+    ) -> str:
         """Given a message instance, serialize it to json
 
         Args:
@@ -343,7 +349,7 @@ def to_json(cls, instance, *, use_integers_for_enums=True) -> str:
         return MessageToJson(
             cls.pb(instance),
             use_integers_for_enums=use_integers_for_enums,
-            including_default_value_fields=True,
+            including_default_value_fields=including_default_value_fields,
         )
 
     def from_json(cls, payload, *, ignore_unknown_fields=False) -> "Message":
diff --git a/tests/test_json.py b/tests/test_json.py
index 34c2d438..4b7be8be 100644
--- a/tests/test_json.py
+++ b/tests/test_json.py
@@ -97,6 +97,29 @@ class Zone(proto.Enum):
     assert json2 == '{"zone":"EPIPELAGIC"}'
 
 
+def test_json_default_values():
+    class Squid(proto.Message):
+        mass_kg = proto.Field(proto.INT32, number=1)
+        name = proto.Field(proto.STRING, number=2)
+
+    s = Squid(name="Steve")
+    json1 = (
+        Squid.to_json(s, including_default_value_fields=False)
+        .replace(" ", "")
+        .replace("\n", "")
+    )
+    assert json1 == '{"name":"Steve"}'
+
+    json2 = Squid.to_json(s).replace(" ", "").replace("\n", "")
+    assert (
+        json2 == '{"name":"Steve","massKg":0}' or json2 == '{"massKg":0,"name":"Steve"}'
+    )
+
+    s1 = Squid.from_json(json1)
+    s2 = Squid.from_json(json2)
+    assert s == s1 == s2
+
+
 def test_json_unknown_field():
     # Note that 'lengthCm' is unknown in the local definition.
     # This could happen if the client is using an older proto definition