diff --git a/cmp/compare.go b/cmp/compare.go
index 119af26..b98a256 100644
--- a/cmp/compare.go
+++ b/cmp/compare.go
@@ -58,8 +58,10 @@ import (
 //
 //   - If the values have an Equal method of the form "(T) Equal(T) bool" or
 //     "(T) Equal(I) bool" where T is assignable to I, then use the result of
-//     x.Equal(y) even if x or y is nil. Otherwise, no such method exists and
-//     evaluation proceeds to the next rule.
+//     x.Equal(y) when both values are non-nil. If either value is nil, Equal
+//     reports whether both are nil without calling the method (so a nil
+//     receiver never panics). Otherwise, no such method exists and evaluation
+//     proceeds to the next rule.
 //
 //   - Lastly, try to compare x and y based on their basic kinds.
 //     Simple kinds like booleans, integers, floats, complex numbers, strings,