diff --git a/broker.go b/broker.go
index eb5bc0bf8..6bdea3869 100644
--- a/broker.go
+++ b/broker.go
@@ -312,7 +312,10 @@ func (b *Broker) decode(pd packetDecoder) (err error) {
 		return err
 	}
 
-	b.addr = fmt.Sprint(host, ":", port)
+	b.addr = net.JoinHostPort(host, fmt.Sprint(port))
+	if _, _, err := net.SplitHostPort(b.addr); err != nil {
+		return err
+	}
 
 	return nil
 }
diff --git a/fetch_response.go b/fetch_response.go
index 1ac543921..840808d68 100644
--- a/fetch_response.go
+++ b/fetch_response.go
@@ -22,6 +22,9 @@ func (pr *FetchResponseBlock) decode(pd packetDecoder) (err error) {
 	if err != nil {
 		return err
 	}
+	if msgSetSize < 0 {
+		return PacketDecodingError{"invalid message set size"}
+	}
 
 	msgSetDecoder, err := pd.getSubset(int(msgSetSize))
 	if err != nil {