diff --git a/xarray/core/dataset.py b/xarray/core/dataset.py
index 8898cff789a..bb2b6461352 100644
--- a/xarray/core/dataset.py
+++ b/xarray/core/dataset.py
@@ -5806,6 +5806,11 @@ def interpolate_na(
         interpolated: Dataset
             Filled in Dataset.
 
+        Warning
+        --------
+        When passing fill_value as a keyword argument with method="linear", it does not use
+        ``numpy.interp`` but it uses ``scipy.interpolate.interp1d``, which provides the fill_value parameter.
+
         See Also
         --------
         numpy.interp