diff --git a/src/lvmapi/routers/transparency.py b/src/lvmapi/routers/transparency.py
index 2ea6aca..2279f0a 100644
--- a/src/lvmapi/routers/transparency.py
+++ b/src/lvmapi/routers/transparency.py
@@ -47,7 +47,7 @@ class TransparencyData(BaseModel):
     zero_point: Annotated[float, Field(description="Zero-point value")]
 
 
-@router.get("/", summary="Transparency measurements")
+@router.get("", summary="Transparency measurements")
 async def route_get_transparency(
     start_time: Annotated[
         float | None,
diff --git a/src/lvmapi/tools/transparency.py b/src/lvmapi/tools/transparency.py
index 174c871..f56d6f3 100644
--- a/src/lvmapi/tools/transparency.py
+++ b/src/lvmapi/tools/transparency.py
@@ -24,13 +24,22 @@ async def get_transparency(start_time: float, end_time: float):
   |> yield(name: "mean")
 """
 
+    SCHEMA: dict[str, polars.DataType] = {
+        "time": polars.Datetime(time_unit="ms", time_zone="UTC"),
+        "telescope": polars.String(),
+        "zero_point": polars.Float32(),
+    }
+
     data = await query_influxdb(query)
 
+    if len(data) == 0:
+        return polars.DataFrame(None, schema=SCHEMA)
+
     # Clean up the dataframe.
     data = data.select(
         time=polars.col._time,
         telescope=polars.col._measurement.str.extract(r"lvm\.([a-z]+)\.guider"),
         zero_point=polars.col._value,
-    )
+    ).cast(SCHEMA)  # type: ignore
 
     return data