diff --git a/src/crypto/rsa/rsa.go b/src/crypto/rsa/rsa.go
index 0715421187d8b1..4fa8d0eab3fd38 100644
--- a/src/crypto/rsa/rsa.go
+++ b/src/crypto/rsa/rsa.go
@@ -58,6 +58,8 @@ func (pub *PublicKey) Size() int {
 }
 
 // Equal reports whether pub and x have the same value.
+//
+// applie only to [*PublicKey], returns false in other cases.
 func (pub *PublicKey) Equal(x crypto.PublicKey) bool {
 	xx, ok := x.(*PublicKey)
 	if !ok {