diff --git a/pyrit/message_normalizer/json_schema_normalizer.py b/pyrit/message_normalizer/json_schema_normalizer.py
index b3a072fd88..f7acc1cfe2 100644
--- a/pyrit/message_normalizer/json_schema_normalizer.py
+++ b/pyrit/message_normalizer/json_schema_normalizer.py
@@ -126,7 +126,7 @@ def _adapt_message(self, *, message: Message) -> Message:
         if not changed:
             return message
 
-        return Message(new_pieces)
+        return Message(message_pieces=new_pieces)
 
     def _adapt_piece(self, *, piece: MessagePiece) -> MessagePiece:
         """
diff --git a/tests/unit/message_normalizer/test_json_schema_normalizer.py b/tests/unit/message_normalizer/test_json_schema_normalizer.py
index abfc399328..eed3ef7679 100644
--- a/tests/unit/message_normalizer/test_json_schema_normalizer.py
+++ b/tests/unit/message_normalizer/test_json_schema_normalizer.py
@@ -46,7 +46,7 @@ class TestJsonSchemaNormalizer:
     async def test_text_piece_gets_schema_appended_to_converted_value(self, normalizer: JsonSchemaNormalizer) -> None:
         schema = {"type": "object", "properties": {"answer": {"type": "string"}}}
         piece = _text_piece(value="Answer the question.", metadata={JSON_SCHEMA_METADATA_KEY: schema})
-        message = Message([piece])
+        message = Message(message_pieces=[piece])
 
         result = await normalizer.normalize_async([message])
         out_piece = result[0].message_pieces[0]
@@ -66,7 +66,7 @@ async def test_text_piece_preserves_other_metadata(self, normalizer: JsonSchemaN
                 "other": 7,
             },
         )
-        result = await normalizer.normalize_async([Message([piece])])
+        result = await normalizer.normalize_async([Message(message_pieces=[piece])])
         new_metadata = result[0].message_pieces[0].prompt_metadata
         assert JSON_SCHEMA_METADATA_KEY not in new_metadata
         assert new_metadata == {"response_format": "json", "other": 7}
@@ -76,7 +76,7 @@ async def test_non_text_piece_only_strips_key(self, normalizer: JsonSchemaNormal
         piece = _image_piece(value="fake.jpg", metadata={JSON_SCHEMA_METADATA_KEY: schema, "extra": "stay"})
         original_converted_value = piece.converted_value
 
-        result = await normalizer.normalize_async([Message([piece])])
+        result = await normalizer.normalize_async([Message(message_pieces=[piece])])
         out_piece = result[0].message_pieces[0]
 
         assert JSON_SCHEMA_METADATA_KEY not in out_piece.prompt_metadata
@@ -87,7 +87,7 @@ async def test_non_text_piece_only_strips_key(self, normalizer: JsonSchemaNormal
 
     async def test_no_schema_is_noop(self, normalizer: JsonSchemaNormalizer) -> None:
         piece = _text_piece(value="just say hi", metadata={"unrelated": True})
-        message = Message([piece])
+        message = Message(message_pieces=[piece])
 
         result = await normalizer.normalize_async([message])
 
@@ -98,7 +98,7 @@ async def test_input_pieces_not_mutated(self, normalizer: JsonSchemaNormalizer)
         schema = {"type": "object"}
         piece = _text_piece(value="hi", metadata={JSON_SCHEMA_METADATA_KEY: schema})
 
-        await normalizer.normalize_async([Message([piece])])
+        await normalizer.normalize_async([Message(message_pieces=[piece])])
 
         # The original piece still carries the schema and its unchanged text.
         assert piece.prompt_metadata == {JSON_SCHEMA_METADATA_KEY: schema}
@@ -117,7 +117,7 @@ async def test_mixed_pieces_in_message_each_handled(self, normalizer: JsonSchema
         )
         no_schema_piece = _text_piece(value="z", metadata={"foo": "bar"}, conversation_id=conversation_id)
 
-        result = await normalizer.normalize_async([Message([text_piece, image_piece, no_schema_piece])])
+        result = await normalizer.normalize_async([Message(message_pieces=[text_piece, image_piece, no_schema_piece])])
         out_pieces = result[0].message_pieces
 
         assert JSON_SCHEMA_METADATA_KEY not in out_pieces[0].prompt_metadata
@@ -133,8 +133,8 @@ async def test_mixed_pieces_in_message_each_handled(self, normalizer: JsonSchema
 
     async def test_multiple_messages(self, normalizer: JsonSchemaNormalizer) -> None:
         schema = {"type": "object"}
-        msg_with_schema = Message([_text_piece(value="a", metadata={JSON_SCHEMA_METADATA_KEY: schema})])
-        msg_without_schema = Message([_text_piece(value="b", metadata={})])
+        msg_with_schema = Message(message_pieces=[_text_piece(value="a", metadata={JSON_SCHEMA_METADATA_KEY: schema})])
+        msg_without_schema = Message(message_pieces=[_text_piece(value="b", metadata={})])
 
         result = await normalizer.normalize_async([msg_with_schema, msg_without_schema])
         assert "### Response format" in result[0].message_pieces[0].converted_value
@@ -155,7 +155,7 @@ async def test_appended_text_lists_schema_keys(self, normalizer: JsonSchemaNorma
         }
         piece = _text_piece(value="prompt", metadata={JSON_SCHEMA_METADATA_KEY: schema})
 
-        result = await normalizer.normalize_async([Message([piece])])
+        result = await normalizer.normalize_async([Message(message_pieces=[piece])])
         appended = result[0].message_pieces[0].converted_value
 
         # Sanity-check that the rendered text actually surfaces schema field names.
@@ -170,7 +170,7 @@ async def test_custom_template_is_used(self) -> None:
         schema = {"type": "object"}
         piece = _text_piece(value="hi", metadata={JSON_SCHEMA_METADATA_KEY: schema})
 
-        result = await normalizer.normalize_async([Message([piece])])
+        result = await normalizer.normalize_async([Message(message_pieces=[piece])])
         out_value = result[0].message_pieces[0].converted_value
 
         assert "<<SCHEMA START>>" in out_value