diff --git a/CHANGELOG.md b/CHANGELOG.md
index 040d34c8..253dad10 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -27,6 +27,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 * `ChatOllama()` can now be created without a `model`, so `ChatOllama().list_models()` works. Sending a message without a model still raises an error that lists the available models. (#166)
 * `ChatGoogle()` now reports `finish_reason == "content_filter"` for Gemini's `IMAGE_SAFETY`, `IMAGE_PROHIBITED_CONTENT`, `IMAGE_RECITATION` and `LANGUAGE` finish reasons, instead of passing the raw Gemini string through, and reports `"tool_use"` (rather than `"success"`) when a turn ends with a tool request, as `ChatOpenAI()` does. (#473)
 * The error raised for a tool request with invalid JSON arguments from `ChatOpenAI()` and `ChatOpenAICompletions()` (and the providers built on them) now shows the offending arguments, instead of the literal text `{args}`.
+* `ChatMistral(seed=0)` now sends `random_seed: 0` instead of silently dropping the seed, and a seed no longer replaces an `extra_body` passed through `kwargs`: Mistral's `random_seed` is merged into it. (#475)
 * `content_image_url()` with a `data:` URL no longer silently drops the `detail` argument: the setting is now carried by inline image content and forwarded to OpenAI's Responses and Chat Completions APIs (regular image URLs already forwarded it). Other providers continue to ignore `detail`. (#467)
 * `ChatBedrock()` on a Converse model no longer drops redacted reasoning blocks when streaming. They were discarded as they arrived, so a streamed turn lost them, while a non-streamed one kept them. (#468)
 * `ChatBedrockAnthropic()` now uses native structured outputs for `data_model` on Claude 4.5 and later, as `ChatAnthropic()` does. Its Bedrock model IDs (`anthropic.claude-...`, `us.anthropic.claude-...`) weren't recognized, so it fell back to forcing a tool call, which Claude Opus 5.5 and Sonnet 5.5 reject with a 400.
diff --git a/chatlas/_provider_mistral.py b/chatlas/_provider_mistral.py
index f7826f17..826bca63 100644
--- a/chatlas/_provider_mistral.py
+++ b/chatlas/_provider_mistral.py
@@ -1,7 +1,7 @@
 from __future__ import annotations
 
 import os
-from typing import TYPE_CHECKING, Optional
+from typing import TYPE_CHECKING, Any, Optional, cast
 
 from ._chat import Chat
 from ._logging import log_model_default
@@ -170,12 +170,16 @@ def _chat_perform_args(
             del kwargs2["stream_options"]
 
         # Mistral wants random_seed, not seed
-        if seed := kwargs2.pop("seed", None):
-            if isinstance(seed, int):
-                kwargs2["extra_body"] = {"random_seed": seed}
-            elif seed is not None:
+        seed = kwargs2.pop("seed", None)
+        if seed is not None:
+            if not isinstance(seed, int):
                 raise ValueError(
                     "MistralProvider only accepts an integer seed, or None."
                 )
+            extra_body: dict[str, Any] = dict(
+                cast("dict[str, Any]", kwargs2.get("extra_body") or {})
+            )
+            extra_body["random_seed"] = seed
+            kwargs2["extra_body"] = extra_body
 
         return kwargs2
diff --git a/tests/test_provider_mistral.py b/tests/test_provider_mistral.py
index bb3c4a41..f5455209 100644
--- a/tests/test_provider_mistral.py
+++ b/tests/test_provider_mistral.py
@@ -78,3 +78,18 @@ def test_data_extraction():
 @pytest.mark.vcr
 def test_mistral_model_list():
     assert_list_models(ChatMistral)
+
+
+def test_mistral_seed_zero_is_sent_as_random_seed():
+    chat = ChatMistral(api_key="key", seed=0)
+    args = chat.provider._chat_perform_args(False, [], {})
+    assert "seed" not in args
+    assert args["extra_body"] == {"random_seed": 0}
+
+
+def test_mistral_seed_keeps_user_extra_body():
+    chat = ChatMistral(api_key="key", seed=7)
+    args = chat.provider._chat_perform_args(
+        False, [], {}, kwargs={"extra_body": {"safe_prompt": True}}
+    )
+    assert args["extra_body"] == {"safe_prompt": True, "random_seed": 7}