diff --git a/doc/openvpn.8 b/doc/openvpn.8
index 42ccd989..f0797998 100644
--- a/doc/openvpn.8
+++ b/doc/openvpn.8
@@ -4577,6 +4577,8 @@ Specify the curve to use for elliptic curve Diffie Hellman. Available
 curves can be listed with
 .BR \-\-show\-curves .
 The specified curve will only be used for ECDH TLS-ciphers.
+
+This option is not supported in mbed TLS builds of OpenVPN.
 .\"*********************************************************
 .TP
 .B \-\-cert file