diff --git a/USAGE b/USAGE
index 35c7923..d18b8b4 100644
--- a/USAGE
+++ b/USAGE
@@ -101,5 +101,8 @@ prompt_attribute - Enable honoring of Prompt attribute sent from server for
                    input. Without this option all user input during 
                    challenge-response will be echoed. See RFC2869 Section 5.10
 
+require_message_authenticator - Discard Access-Accept, Access-Challenge, and
+		Access-Reject packets which do not contain Message-Authenticator.
+
 ---------------------------------------------------------------------------
 
diff --git a/src/pam_radius_auth.c b/src/pam_radius_auth.c
index 3fe2834..1d957a3 100644
--- a/src/pam_radius_auth.c
+++ b/src/pam_radius_auth.c
@@ -197,6 +197,9 @@ static int _pam_parse(int argc, CONST char **argv, radius_conf_t *conf)
 		} else if (!strcmp(arg, "privilege_level")) {
 			conf->privilege_level = TRUE;
 
+		} else if (!strcmp(arg, "require_message_authenticator")) {
+			conf->require_message_authenticator = TRUE;
+
 		} else {
 			_pam_log(LOG_WARNING, "unrecognized option '%s'", arg);
 		}
@@ -435,7 +438,7 @@ static void get_accounting_vector(AUTH_HDR *request, radius_server_t *server)
 /**
  * Verify the response from the server
  */
-static int verify_packet(radius_server_t *server, AUTH_HDR *response, AUTH_HDR *request)
+static int verify_packet(radius_server_t *server, AUTH_HDR *response, AUTH_HDR *request, radius_conf_t *conf)
 {
 	MD5_CTX my_md5;
 	uint8_t calculated[AUTH_VECTOR_LEN];
@@ -470,6 +473,10 @@ static int verify_packet(radius_server_t *server, AUTH_HDR *response, AUTH_HDR *
 		attr += attr[1];
 	}
 
+	if ((request->code == PW_ACCESS_REQUEST) && conf->require_message_authenticator && !message_authenticator) {
+		return FALSE;
+	}
+
 	/*
 	 * We could dispense with the memcpy, and do MD5's of the packet
 	 * + vector piece by piece.	This is easier understand, and maybe faster.
@@ -1242,7 +1249,7 @@ static int talk_radius(radius_conf_t *conf, AUTH_HDR *request, AUTH_HDR *respons
 					continue;
 				}
 
-				if (!verify_packet(server, response, request)) {
+				if (!verify_packet(server, response, request, conf)) {
 					_pam_log(LOG_ERR, "packet from RADIUS server %s failed verification: "
 						 "The shared secret is probably incorrect.", server->hostname);
 					continue;
diff --git a/src/pam_radius_auth.h b/src/pam_radius_auth.h
index a18f321..acecb4d 100644
--- a/src/pam_radius_auth.h
+++ b/src/pam_radius_auth.h
@@ -188,6 +188,7 @@ typedef struct radius_conf_t {
 	char prompt[MAXPROMPT];
 	int prompt_attribute;
 	int privilege_level;
+	int require_message_authenticator;
 	uint8_t *message_authenticator;
 } radius_conf_t;