diff --git a/litellm/llms/soniox/audio_transcription/handler.py b/litellm/llms/soniox/audio_transcription/handler.py
index 1725132829e..cfb3ec75311 100644
--- a/litellm/llms/soniox/audio_transcription/handler.py
+++ b/litellm/llms/soniox/audio_transcription/handler.py
@@ -39,7 +39,9 @@ from litellm.llms.custom_httpx.http_handler import (
 from litellm.llms.soniox.audio_transcription.transformation import (
     SONIOX_HANDLER_ONLY_PARAMS,
     SonioxAudioTranscriptionConfig,
+    SonioxInvalidBoolParam,
     decode_soniox_form_params,
+    raise_soniox_form_error,
 )
 from litellm.llms.soniox.common_utils import (
     SONIOX_DEFAULT_CLEANUP,
@@ -228,6 +230,8 @@ class SonioxAudioTranscriptionHandler:
         base_url: Final = get_soniox_api_base(api_base)
 
         decoded: Final = decode_soniox_form_params(optional_params)
+        if isinstance(decoded, SonioxInvalidBoolParam):
+            raise_soniox_form_error(decoded)
 
         # Server-side clamps. Caller-supplied poll settings (from request kwargs)
         # are bounded so an authenticated caller cannot force a worker into a
diff --git a/litellm/llms/soniox/audio_transcription/transformation.py b/litellm/llms/soniox/audio_transcription/transformation.py
index 9f224944073..dbe5d1cd746 100644
--- a/litellm/llms/soniox/audio_transcription/transformation.py
+++ b/litellm/llms/soniox/audio_transcription/transformation.py
@@ -10,8 +10,9 @@ contract of `base_llm_http_handler.audio_transcriptions`.
 """
 
 from collections.abc import Mapping
+from dataclasses import dataclass
 from types import MappingProxyType
-from typing import Any, Final
+from typing import Any, Final, NoReturn
 
 from httpx import Headers, Response
 from pydantic import TypeAdapter, ValidationError
@@ -68,7 +69,19 @@ SONIOX_BOOL_PARAMS: Final[frozenset[str]] = frozenset(
 _JSON_CONTAINER: Final = TypeAdapter[dict[str, object] | list[object]](dict[str, object] | list[object])
 
 
-def _decode_form_value(key: str, value: object) -> object:
+@dataclass(frozen=True, slots=True)
+class SonioxInvalidBoolParam:
+    key: str
+    value: str
+
+
+def raise_soniox_form_error(error: SonioxInvalidBoolParam) -> NoReturn:
+    raise SonioxException(
+        message=f"`{error.key}` must be a boolean, got {error.value!r}", status_code=400, headers=None
+    )
+
+
+def _decode_form_value(key: str, value: object) -> object | SonioxInvalidBoolParam:
     if not isinstance(value, str):
         return value
     if key in SONIOX_BOOL_PARAMS:
@@ -77,7 +90,7 @@ def _decode_form_value(key: str, value: object) -> object:
             return True
         if lowered in ("false", "0"):
             return False
-        raise SonioxException(message=f"`{key}` must be a boolean, got {value!r}", status_code=400, headers=None)
+        return SonioxInvalidBoolParam(key=key, value=value)
     if key in SONIOX_JSON_PARAMS and value.lstrip()[:1] in ("{", "["):
         try:
             return _JSON_CONTAINER.validate_json(value)
@@ -88,9 +101,15 @@ def _decode_form_value(key: str, value: object) -> object:
     return value
 
 
-def decode_soniox_form_params(optional_params: Mapping[str, object]) -> Mapping[str, object]:
+def decode_soniox_form_params(
+    optional_params: Mapping[str, object],
+) -> Mapping[str, object] | SonioxInvalidBoolParam:
     """Multipart form fields reach the proxy as strings; restore the JSON types Soniox expects."""
-    return MappingProxyType({key: _decode_form_value(key, value) for key, value in optional_params.items()})
+    decoded: Final = {key: _decode_form_value(key, value) for key, value in optional_params.items()}
+    return next(
+        (value for value in decoded.values() if isinstance(value, SonioxInvalidBoolParam)),
+        MappingProxyType(decoded),
+    )
 
 
 class SonioxAudioTranscriptionConfig(BaseAudioTranscriptionConfig):
diff --git a/tests/test_litellm/llms/soniox/audio_transcription/test_soniox_audio_transcription_handler.py b/tests/test_litellm/llms/soniox/audio_transcription/test_soniox_audio_transcription_handler.py
index 077b9142d6e..d3b219c5f02 100644
--- a/tests/test_litellm/llms/soniox/audio_transcription/test_soniox_audio_transcription_handler.py
+++ b/tests/test_litellm/llms/soniox/audio_transcription/test_soniox_audio_transcription_handler.py
@@ -339,6 +339,24 @@ class TestPollLimitsClamping:
     a worker on tight poll loops.
     """
 
+    def test_should_raise_400_when_form_bool_param_is_invalid(self):
+        handler = SonioxAudioTranscriptionHandler()
+        with pytest.raises(SonioxException) as exc_info:
+            handler._prepare(
+                audio_file=None,
+                optional_params={
+                    "enable_speaker_diarization": "yes",
+                    "audio_url": "https://example.com/a.wav",
+                },
+                litellm_params={},
+                api_key="sk-test",
+                api_base=None,
+                provider_config=SonioxAudioTranscriptionConfig(),
+                headers={},
+            )
+        assert exc_info.value.status_code == 400
+        assert "enable_speaker_diarization" in str(exc_info.value)
+
     def test_should_clamp_poll_interval_to_minimum(self):
         from litellm.llms.soniox.common_utils import SONIOX_MIN_POLL_INTERVAL
 
diff --git a/tests/test_litellm/llms/soniox/audio_transcription/test_soniox_audio_transcription_transformation.py b/tests/test_litellm/llms/soniox/audio_transcription/test_soniox_audio_transcription_transformation.py
index 99d7c3d4411..2b938f0bb9b 100644
--- a/tests/test_litellm/llms/soniox/audio_transcription/test_soniox_audio_transcription_transformation.py
+++ b/tests/test_litellm/llms/soniox/audio_transcription/test_soniox_audio_transcription_transformation.py
@@ -9,7 +9,9 @@ import pytest
 
 from litellm.llms.soniox.audio_transcription.transformation import (
     SonioxAudioTranscriptionConfig,
+    SonioxInvalidBoolParam,
     decode_soniox_form_params,
+    raise_soniox_form_error,
 )
 from litellm.llms.soniox.common_utils import SonioxException
 from litellm.llms.soniox.types import (
@@ -751,11 +753,16 @@ class TestDecodeSonioxFormParams:
             "language_hints_strict": expected,
         }
 
-    def test_should_raise_400_on_non_boolean_string(self):
+    def test_should_return_error_value_on_non_boolean_string(self):
+        result = decode_soniox_form_params({"context": '{"general": []}', "enable_speaker_diarization": "yes"})
+        assert result == SonioxInvalidBoolParam(key="enable_speaker_diarization", value="yes")
+
+    def test_should_map_invalid_bool_error_to_400(self):
         with pytest.raises(SonioxException) as exc_info:
-            decode_soniox_form_params({"enable_speaker_diarization": "yes"})
+            raise_soniox_form_error(SonioxInvalidBoolParam(key="enable_speaker_diarization", value="yes"))
         assert exc_info.value.status_code == 400
         assert "enable_speaker_diarization" in str(exc_info.value)
+        assert "yes" in str(exc_info.value)
 
     @pytest.mark.parametrize(
         "raw, expected",