diff --git a/avr/recv.c b/avr/recv.c
index 55b6634..7de9035 100644
--- a/avr/recv.c
+++ b/avr/recv.c
@@ -22,7 +22,7 @@ ISR(SPI_STC_vect) {
     switch (i) {
         case 0: {
             if (in == TABBY_PRINTER_SYNC_1) {
-                header.data[0] = in;
+                header.preamble[0] = in;
                 i++;
 
                 b = 0;
@@ -33,7 +33,7 @@ ISR(SPI_STC_vect) {
 
         case 1: {
             if (in == TABBY_PRINTER_SYNC_2) {
-                header.data[1] = in;
+                header.preamble[1] = in;
                 i++;
             } else {
                 i = 0;
@@ -67,6 +67,10 @@ ISR(SPI_STC_vect) {
             header.size |= in << 8;
             i++;
 
+            if (header.size > TABBY_PRINTER_PACKET_MAX_SIZE) {
+                i = 0;
+            }
+
             break;
         }
 
@@ -79,6 +83,8 @@ ISR(SPI_STC_vect) {
                 out = TABBY_PRINTER_DEVICE_ID;
             } else if (b == header.size + 2) {
                 b++;
+
+                out = TABBY_PRINTER_OK;
             } else if (b == header.size + 3) {
                 i = 0;
             }