diff --git a/coloraide/interpolate/__init__.py b/coloraide/interpolate/__init__.py
index b80951ba..043e0a96 100644
--- a/coloraide/interpolate/__init__.py
+++ b/coloraide/interpolate/__init__.py
@@ -320,6 +320,7 @@ def steps(
         return [i[1] for i in ret]
 
     def premultiply(self, coords: Vector, alpha: float | None = None) -> None:
+        """Apply premultiplication to semi-transparent colors."""
 
         if alpha is not None:
             coords[-1] = alpha