diff --git a/sungrow.go b/sungrow.go
index 3e4f212..b4cef28 100644
--- a/sungrow.go
+++ b/sungrow.go
@@ -61,12 +61,15 @@ func (c *sungrowConn) Write(msg []byte) (int, error) {
 
 	bs := c.block.BlockSize()
 	padlen := bs - (len(msg) % bs)
+	if padlen == bs {
+		padlen = 0
+	}
 
 	req := make([]byte, 4+len(msg)+padlen)
 	copy(req, []byte{1, 0, byte(len(msg)), byte(padlen)}) // 4 byte encryption header
 	copy(req[4:], header)                                 // 2 byte sungrow header, replaces txid
 	copy(req[6:], msg[2:])                                // rest of message
-	copy(req[4+len(msg):], padding)                       // padding
+	copy(req[4+len(msg):], padding[:padlen])              // padding
 
 	// ECB mode.........
 	for cp := req[4:]; len(cp) > 0; cp = cp[bs:] {
@@ -93,13 +96,16 @@ func (c *sungrowConn) Read(out []byte) (int, error) {
 		return 0, err
 	}
 	pktlen, padlen := int(hdr[2]), int(hdr[3])
+	bs := c.block.BlockSize()
+	if (pktlen+padlen)%bs != 0 {
+		return 0, fmt.Errorf("pktlen + padlen = %d + %d = %d, want divisble by %d", pktlen, padlen, pktlen+padlen, bs)
+	}
 	pkt := make([]byte, pktlen+padlen)
 	if _, err := io.ReadFull(c.Conn, pkt); err != nil {
 		return 0, err
 	}
 
 	// ECB mode here too.........
-	bs := c.block.BlockSize()
 	for cp := pkt; len(cp) > 0; cp = cp[bs:] {
 		c.block.Decrypt(cp, cp)
 	}