diff --git a/docs/handbook/image-file-formats.rst b/docs/handbook/image-file-formats.rst
index ffc94914873..9c2319b44e3 100644
--- a/docs/handbook/image-file-formats.rst
+++ b/docs/handbook/image-file-formats.rst
@@ -1127,6 +1127,7 @@ The :py:meth:`~PIL.Image.Image.save` method supports the following options:
 **exact**
     If true, preserve the transparent RGB values. Otherwise, discard
     invisible RGB values for better compression. Defaults to false.
+    Requires LibWebP 0.5.0 or later.
 
 **icc_profile**
     The ICC Profile to include in the saved file. Only supported if