diff --git a/ChangeLog.md b/ChangeLog.md
index a5eb8958998..68a68746977 100644
--- a/ChangeLog.md
+++ b/ChangeLog.md
@@ -1,5 +1,14 @@
 # Change Log
 
+### 2020-xx-xx - 5.4.2
+Autorest core version: 3.0.6320
+
+Modelerfour version: 4.15.421
+
+**Bug Fixes**
+
+- Set discriminator value in cases where discriminator is readonly  #815
+
 ### 2020-11-03 - 5.4.1
 Autorest core version: 3.0.6318
 
diff --git a/autorest/codegen/serializers/model_generic_serializer.py b/autorest/codegen/serializers/model_generic_serializer.py
index 61e9c283677..29c9e9354ef 100644
--- a/autorest/codegen/serializers/model_generic_serializer.py
+++ b/autorest/codegen/serializers/model_generic_serializer.py
@@ -26,15 +26,15 @@ def init_args(model: ObjectSchema) -> List[str]:
         init_args.append(f"super({model.name}, self).__init__(**kwargs)")
 
         for prop in ModelGenericSerializer.get_properties_to_initialize(model):
-            if prop.readonly:
-                init_args.append(f"self.{prop.name} = None")
-            elif prop.is_discriminator:
+            if prop.is_discriminator:
                 discriminator_value = f"'{model.discriminator_value}'" if model.discriminator_value else None
                 if not discriminator_value:
                     typing = "Optional[str]"
                 else:
                     typing = "str"
                 init_args.append(f"self.{prop.name} = {discriminator_value}  # type: {typing}")
+            elif prop.readonly:
+                init_args.append(f"self.{prop.name} = None")
             elif not prop.constant:
                 if prop.required and not prop.default_value:
                     init_args.append(f"self.{prop.name} = kwargs['{prop.name}']")
diff --git a/autorest/codegen/serializers/model_python3_serializer.py b/autorest/codegen/serializers/model_python3_serializer.py
index 8425748ea2e..aaacda5494d 100644
--- a/autorest/codegen/serializers/model_python3_serializer.py
+++ b/autorest/codegen/serializers/model_python3_serializer.py
@@ -55,15 +55,15 @@ def init_args(model: ObjectSchema) -> List[str]:
         else:
             init_args.append(f"super({model.name}, self).__init__(**kwargs)")
         for prop in ModelPython3Serializer.get_properties_to_initialize(model):
-            if prop.readonly:
-                init_args.append(f"self.{prop.name} = None")
-            elif prop.is_discriminator:
+            if prop.is_discriminator:
                 discriminator_value = f"'{model.discriminator_value}'" if model.discriminator_value else None
                 if not discriminator_value:
                     typing = "Optional[str]"
                 else:
                     typing = "str"
                 init_args.append(f"self.{prop.name} = {discriminator_value}  # type: {typing}")
+            elif prop.readonly:
+                init_args.append(f"self.{prop.name} = None")
             elif not prop.constant:
                 init_args.append(f"self.{prop.name} = {prop.name}")