diff --git a/avr/ringbuffer.asm b/avr/ringbuffer.asm
index a5bb5c9..a4abbe6 100644
--- a/avr/ringbuffer.asm
+++ b/avr/ringbuffer.asm
@@ -49,6 +49,9 @@ RingBuffer_Alloc:
   ldd r18, y+RINGBUFFER_OFFS_USED
   ldd r19, y+RINGBUFFER_OFFS_WRITEPOS
   
+  cpi r16, 2                             ; alloc at least two bytes
+  brcs RingBuffer_Alloc_error            ; too few bytes
+  
   mov r20, r16                           ; to_alloc
   add r20, r18                           ; to_alloc + used
   cp r20, r17                            ; new_used < max?
@@ -70,7 +73,8 @@ RingBuffer_Alloc_l1:
       clr r17
       add yl, r16
       adc yh, r17
-      st y+RINGBUFFER_OFFS_DATA, r17
+      std y+RINGBUFFER_OFFS_DATA, r17     ; (length byte in COM module)
+      std y+RINGBUFFER_OFFS_DATA+1, r17   ; (flags byte in COM module)
     pop yh
   pop yl