diff --git a/pyecobee/__init__.py b/pyecobee/__init__.py
index 054976e..3ba9317 100644
--- a/pyecobee/__init__.py
+++ b/pyecobee/__init__.py
@@ -259,7 +259,13 @@ def set_fan_mode(
         hold_type: str,
         **optional_arg,
     ) -> None:
-        """Sets the fan mode (auto, minontime, on)."""
+        """
+        Sets the fan mode (auto, minontime, on).
+            valid optional_arg
+                holdHours - required if HoldType is holdHours
+                coolHoldTemp
+                heatHoldTemp
+        """
         body = {
             "selection": {
                 "selectionType": "thermostats",