diff --git a/pkg/apis/certmanager/v1alpha2/types_certificate.go b/pkg/apis/certmanager/v1alpha2/types_certificate.go
index 2c5aa9217..258e4a807 100644
--- a/pkg/apis/certmanager/v1alpha2/types_certificate.go
+++ b/pkg/apis/certmanager/v1alpha2/types_certificate.go
@@ -79,6 +79,7 @@ type CertificateSpec struct {
 	// CommonName is a common name to be used on the Certificate.
 	// The CommonName should have a length of 64 characters or fewer to avoid
 	// generating invalid CSRs.
+	// This value is ignored by TLS clients when any subject alt name is set.
 	// +optional
 	CommonName string `json:"commonName,omitempty"`