diff --git a/doc/reference.conf b/doc/reference.conf
index 66e738bd..995075df 100644
--- a/doc/reference.conf
+++ b/doc/reference.conf
@@ -1418,7 +1418,12 @@ general {
 	 * The spki_* variants operate on the SubjectPublicKeyInfo of the certificate, which does
 	 * not change unless the private key is changed.  This allows the fingerprint to stay
 	 * constant even if the certificate is reissued.  These fingerprints will be prefixed with
-	 * "SPKI:SHA2-256:" or "SPKI:SHA2-512:" depending on the hash type.
+	 * "SPKI:SHA2-256:" or "SPKI:SHA2-512:" depending on the hash type.  These fingerprints
+	 * are not supported on servers running charybdis 3.5 or earlier.
+	 *
+	 * To generate a fingerprint from a certificate file, please use the mkfingerprint utility
+	 * program located in the bin/ subdirectory of your IRCd installation. Running it with no
+	 * arguments will give you a brief usage message; it takes method and filename arguments.
 	 */
 	certfp_method = spki_sha256;