diff --git a/src/faster_whisper_server/routers/stt.py b/src/faster_whisper_server/routers/stt.py
index f55bf0d9..a39b5686 100644
--- a/src/faster_whisper_server/routers/stt.py
+++ b/src/faster_whisper_server/routers/stt.py
@@ -9,6 +9,7 @@
     APIRouter,
     Form,
     Query,
+    Request,
     Response,
     UploadFile,
     WebSocket,
@@ -30,6 +31,8 @@
 from faster_whisper_server.core import Segment, segments_to_srt, segments_to_text, segments_to_vtt
 from faster_whisper_server.dependencies import ConfigDependency, ModelManagerDependency, get_config
 from faster_whisper_server.server_models import (
+    DEFAULT_TIMESTAMP_GRANULARITIES,
+    TIMESTAMP_GRANULARITIES_COMBINATIONS,
     TimestampGranularities,
     TranscriptionJsonResponse,
     TranscriptionVerboseJsonResponse,
@@ -150,6 +153,18 @@ def translate_file(
         return segments_to_response(segments, transcription_info, response_format)
 
 
+# HACK: Since Form() doesn't support `alias`, we need to use a workaround.
+async def get_timestamp_granularities(request: Request) -> TimestampGranularities:
+    form = await request.form()
+    if form.get("timestamp_granularities[]") is None:
+        return DEFAULT_TIMESTAMP_GRANULARITIES
+    timestamp_granularities = form.getlist("timestamp_granularities[]")
+    assert (
+        timestamp_granularities in TIMESTAMP_GRANULARITIES_COMBINATIONS
+    ), f"{timestamp_granularities} is not a valid value for `timestamp_granularities[]`."
+    return timestamp_granularities
+
+
 # https://platform.openai.com/docs/api-reference/audio/createTranscription
 # https://github.com/openai/openai-openapi/blob/master/openapi.yaml#L8915
 @router.post(
@@ -159,6 +174,7 @@ def translate_file(
 def transcribe_file(
     config: ConfigDependency,
     model_manager: ModelManagerDependency,
+    request: Request,
     file: Annotated[UploadFile, Form()],
     model: Annotated[ModelName | None, Form()] = None,
     language: Annotated[Language | None, Form()] = None,
@@ -167,6 +183,7 @@ def transcribe_file(
     temperature: Annotated[float, Form()] = 0.0,
     timestamp_granularities: Annotated[
         TimestampGranularities,
+        # WARN: `alias` doesn't actually work.
         Form(alias="timestamp_granularities[]"),
     ] = ["segment"],
     stream: Annotated[bool, Form()] = False,
@@ -178,6 +195,11 @@ def transcribe_file(
         language = config.default_language
     if response_format is None:
         response_format = config.default_response_format
+    timestamp_granularities = asyncio.run(get_timestamp_granularities(request))
+    if timestamp_granularities != DEFAULT_TIMESTAMP_GRANULARITIES and response_format != ResponseFormat.VERBOSE_JSON:
+        logger.warning(
+            "It only makes sense to provide `timestamp_granularities[]` when `response_format` is set to `verbose_json`. See https://platform.openai.com/docs/api-reference/audio/createTranscription#audio-createtranscription-timestamp_granularities."  # noqa: E501
+        )
     whisper = model_manager.load_model(model)
     segments, transcription_info = whisper.transcribe(
         file.file,
diff --git a/src/faster_whisper_server/server_models.py b/src/faster_whisper_server/server_models.py
index 33d17206..b6cf5aa4 100644
--- a/src/faster_whisper_server/server_models.py
+++ b/src/faster_whisper_server/server_models.py
@@ -29,7 +29,7 @@ class TranscriptionVerboseJsonResponse(BaseModel):
     language: str
     duration: float
     text: str
-    words: list[Word]
+    words: list[Word] | None
     segments: list[Segment]
 
     @classmethod
@@ -38,7 +38,7 @@ def from_segment(cls, segment: Segment, transcription_info: TranscriptionInfo) -
             language=transcription_info.language,
             duration=segment.end - segment.start,
             text=segment.text,
-            words=(segment.words if isinstance(segment.words, list) else []),
+            words=segment.words if transcription_info.transcription_options.word_timestamps else None,
             segments=[segment],
         )
 
@@ -51,7 +51,7 @@ def from_segments(
             duration=transcription_info.duration,
             text=segments_to_text(segments),
             segments=segments,
-            words=Word.from_segments(segments),
+            words=Word.from_segments(segments) if transcription_info.transcription_options.word_timestamps else None,
         )
 
     @classmethod
@@ -112,6 +112,7 @@ class ModelObject(BaseModel):
 TimestampGranularities = list[Literal["segment", "word"]]
 
 
+DEFAULT_TIMESTAMP_GRANULARITIES: TimestampGranularities = ["segment"]
 TIMESTAMP_GRANULARITIES_COMBINATIONS: list[TimestampGranularities] = [
     [],  # should be treated as ["segment"]. https://platform.openai.com/docs/api-reference/audio/createTranscription#audio-createtranscription-timestamp_granularities
     ["segment"],
diff --git a/tests/api_timestamp_granularities_test.py b/tests/api_timestamp_granularities_test.py
new file mode 100644
index 00000000..79a556b3
--- /dev/null
+++ b/tests/api_timestamp_granularities_test.py
@@ -0,0 +1,43 @@
+"""See `tests/openai_timestamp_granularities_test.py` to understand how OpenAI handles `response_type` and `timestamp_granularities`."""  # noqa: E501
+
+from faster_whisper_server.server_models import TIMESTAMP_GRANULARITIES_COMBINATIONS, TimestampGranularities
+from openai import AsyncOpenAI
+import pytest
+
+
+@pytest.mark.asyncio()
+@pytest.mark.parametrize("timestamp_granularities", TIMESTAMP_GRANULARITIES_COMBINATIONS)
+async def test_api_json_response_format_and_timestamp_granularities_combinations(
+    openai_client: AsyncOpenAI,
+    timestamp_granularities: TimestampGranularities,
+) -> None:
+    audio_file = open("audio.wav", "rb")  # noqa: SIM115, ASYNC230
+
+    await openai_client.audio.transcriptions.create(
+        file=audio_file, model="whisper-1", response_format="json", timestamp_granularities=timestamp_granularities
+    )
+
+
+@pytest.mark.asyncio()
+@pytest.mark.parametrize("timestamp_granularities", TIMESTAMP_GRANULARITIES_COMBINATIONS)
+async def test_api_verbose_json_response_format_and_timestamp_granularities_combinations(
+    openai_client: AsyncOpenAI,
+    timestamp_granularities: TimestampGranularities,
+) -> None:
+    audio_file = open("audio.wav", "rb")  # noqa: SIM115, ASYNC230
+
+    transcription = await openai_client.audio.transcriptions.create(
+        file=audio_file,
+        model="whisper-1",
+        response_format="verbose_json",
+        timestamp_granularities=timestamp_granularities,
+    )
+
+    assert transcription.__pydantic_extra__
+    if "word" in timestamp_granularities:
+        assert transcription.__pydantic_extra__.get("segments") is not None
+        assert transcription.__pydantic_extra__.get("words") is not None
+    else:
+        # Unless explicitly requested, words are not present
+        assert transcription.__pydantic_extra__.get("segments") is not None
+        assert transcription.__pydantic_extra__.get("words") is None