diff --git a/vendor/google.golang.org/grpc/attributes/attributes.go b/vendor/google.golang.org/grpc/attributes/attributes.go
index 6ff2792..ae13dda 100644
--- a/vendor/google.golang.org/grpc/attributes/attributes.go
+++ b/vendor/google.golang.org/grpc/attributes/attributes.go
@@ -69,7 +69,9 @@
 // bool' is implemented for a value in the attributes, it is called to
 // determine if the value matches the one stored in the other attributes.  If
 // Equal is not implemented, standard equality is used to determine if the two
-// values are equal.
+// values are equal. Note that some types (e.g. maps) aren't comparable by
+// default, so they must be wrapped in a struct, or in an alias type, with Equal
+// defined.
 func (a *Attributes) Equal(o *Attributes) bool {
 	if a == nil && o == nil {
 		return true