diff --git a/draft-ymbk-lsvr-l3dl-signing.txt b/draft-ymbk-lsvr-l3dl-signing.txt
index 57d07c4..0dd3510 100644
--- a/draft-ymbk-lsvr-l3dl-signing.txt
+++ b/draft-ymbk-lsvr-l3dl-signing.txt
@@ -234,11 +234,11 @@ Internet-Draft   Layer 3 Discovery and Liveness Signing         May 2020
 
 3.  Public Key Infrastructure Method
 
-   Using a PKI is almost the same as using TOFU, but with one additional
-   step: during verification of an OPEN PDU, after extracting the Key
-   field from the PDU but before attempting to use it to verify the
-   PDU's signature, the receiver MUST verify the received key against
-   the PKI to confirm that it's an authorized key.
+   Using a PKI, [RFC5280], is almost the same as using TOFU, but with
+   one additional step: during verification of an OPEN PDU, after
+   extracting the Key field from the PDU but before attempting to use it
+   to verify the PDU's signature, the receiver MUST verify the received
+   key against the PKI to confirm that it's an authorized key.
 
    Generating an OPEN PDU using the PKI method requires a certificate,
    which must be supplied via out of band configuration.  The