diff --git a/client/client_shared.c b/client/client_shared.c
index d704f2bc..3e6d0027 100644
--- a/client/client_shared.c
+++ b/client/client_shared.c
@@ -1613,6 +1613,10 @@ static int mosquitto__parse_socks_url(struct mosq_config *cfg, char *url)
 	start = 0;
 	for(i=0; i<strlen(str); i++){
 		if(str[i] == '['){
+			if(host){
+				err_printf(cfg, "Error: Duplicate IPv6 address.\n");
+				goto cleanup;
+			}
 			in_ipv6_address = true;
 			start = i+1;
 		}else if(str[i] == ']'){