diff --git a/test/fixtures/keys/Makefile b/test/fixtures/keys/Makefile
index 8fc3624982fb27..d953e83c2d6faa 100644
--- a/test/fixtures/keys/Makefile
+++ b/test/fixtures/keys/Makefile
@@ -651,6 +651,9 @@ I_AM_THE_WALRUS_sha256_signature_signedby_rsa_private_b.sha256: rsa_private_b.pe
 rsa_public_b.pem: rsa_private_b.pem
 	openssl rsa -in rsa_private_b.pem -pubout -out rsa_public_b.pem
 
+# The following 'foafssl' cert is used in test/parallel/test-https-foafssl.js.
+# It requires a SAN like 'http://example.com/#me'. More info here:
+# https://www.w3.org/wiki/Foaf+ssl
 rsa_cert_foafssl_b.crt: rsa_private_b.pem
 	openssl req -new -x509 -config rsa_cert_foafssl_b.cnf -key rsa_private_b.pem -out rsa_cert_foafssl_b.crt
 
diff --git a/test/fixtures/keys/rsa_cert_foafssl_b.cnf b/test/fixtures/keys/rsa_cert_foafssl_b.cnf
index 38d6dd36f7bf22..5e69db885a5ab7 100644
--- a/test/fixtures/keys/rsa_cert_foafssl_b.cnf
+++ b/test/fixtures/keys/rsa_cert_foafssl_b.cnf
@@ -1,3 +1,7 @@
+# The following 'foafssl' cert is used in test/parallel/test-https-foafssl.js.
+# It requires a SAN like 'http://example.com/#me'. More info here:
+# https://www.w3.org/wiki/Foaf+ssl
+
 [ req ]
 days                   = 99999
 distinguished_name     = req_distinguished_name