diff --git a/resizer.go b/resizer.go
index 6aa0de3..2316be2 100644
--- a/resizer.go
+++ b/resizer.go
@@ -172,6 +172,7 @@ func applyDefaults(o Options, imageType ImageType) Options {
 		o.Interpretation = InterpretationSRGB
 	}
 	if o.Palette {
+		// Default value of effort in libvips is 7.
 		o.Speed = 3
 	}
 	return o