diff --git a/dnsbl.js b/dnsbl.js
index 3744012692..9a8ed39553 100644
--- a/dnsbl.js
+++ b/dnsbl.js
@@ -2,15 +2,16 @@ var dns = require('dns');
 
 var blocklist = 'zen.spamhaus.org';
 
+var dnsblCache = {};
+
 exports.query = function queryDnsbl(ip, callback) {
+	if (ip in dnsblCache) {
+		callback(dnsblCache[ip]);
+		return;
+	}
 	var reversedIp = ip.split('.').reverse().join('.');
 	dns.resolve4(reversedIp+'.'+blocklist, function(err, addresses) {
-		if (err) {
-			// not on blacklist
-			callback(false);
-		} else {
-			// on blacklist
-			callback(true);
-		}
+		var isBlocked = dnsblCache[ip] = !err;
+		callback(isBlocked);
 	});
 }