diff --git a/avr/modules/flash/flash1pmega.asm b/avr/modules/flash/flash1pmega.asm
index 2066e18..1b33007 100644
--- a/avr/modules/flash/flash1pmega.asm
+++ b/avr/modules/flash/flash1pmega.asm
@@ -42,13 +42,14 @@ flash1pMegaWritePage:
   ldi xl, LOW(flashPageBuffer)
   ldi xh, HIGH(flashPageBuffer)
   ldi r24, LOW(PAGESIZE)
+  ldi r25, HIGH(PAGESIZE)
 flash1pMegaWritePages_loop:
     ld r0, X+                               ; read source data from buffer (low)
     ld r1, X+                               ; read source data from buffer (high)
     ldi r20, (1<<SPMEN)                     ; enable next SPM, write R1:R0 into temp page buffer
     rcall flashDoSpm                        ; (R16)
     adiw zh:zl, 2
-    dec r24
+    sbiw r25:r24, 1
   brne flash1pMegaWritePages_loop
 
   subi zl, LOW(PAGESIZE*2)                  ; point back to begin of page
diff --git a/avr/modules/flash/flashxp.asm b/avr/modules/flash/flashxp.asm
index de805cd..ace7502 100644
--- a/avr/modules/flash/flashxp.asm
+++ b/avr/modules/flash/flashxp.asm
@@ -7,6 +7,8 @@
 ; * Please see toplevel file COPYING of that project for license details.   *
 ; ***************************************************************************
 
+; Code for large pagesizes (128 and larger)
+
 
 ; ***************************************************************************
 ; code
@@ -92,7 +94,7 @@ flashWriteData:
 flashWriteData_beginPage:
   rcall flashBeginPage                 ; (r16, r24, r25, X)
 flashWriteData_calcPosAndLength:
-  rcall flashCalcPosAndLength          ; r18=bytes_to_write, x=pos_in_buffer (r24, r25)
+  rcall flashCalcPosAndLength          ; r18=bytes_to_write, x=pos_in_buffer (r19, r24, r25)
   ; X=abs pos in buffer, r18=bytes to read, r17=bytes initially requested
   ; prepare data for return
   sub r17, r18                         ; r17 holds remainder
@@ -117,24 +119,30 @@ flashWriteData_copyLoop:
 ; @param  R17 number of bytes to write
 ; @return X   absolute write position inside buffer
 ; @return R18 bytes to write
-; @clobbers r24, r25
+; @clobbers r19, r24, r25
 
 flashCalcPosAndLength:
   ; calc offset into buffer
   mov r24, zl
-  andi r24, (FLASH_PAGESIZE-1)   ; r24=rel pos inside buffer
-  ldi r25, FLASH_PAGESIZE
-  sub r25, r24                   ; r25=bytes left inside page
-  mov r18, r17
-  cp r25, r17                    ; bytes to read > bytes left in page?
-  brcc flashCalcPosAndLength_l1  ; no: jump
-  mov r18, r25                   ; yes: cut r18 to number of bytes left in page
-flashCalcPosAndLength_l1:
-  ldi xl, LOW(flashPageBuffer)   ; set X to pos within page buffer
+  mov r25, zh
+  andi r24, LOW(FLASH_PAGESIZE-1)
+  andi r25, HIGH(FLASH_PAGESIZE-1)   ; R25:r24=pos inside page
+  ldi r18, LOW(FLASH_PAGESIZE)
+  ldi r19, HIGH(FLASH_PAGESIZE)
+  sub r18, r24
+  sbc r19, r25                       ; R19:R18=FLASH_PAGESIZE-relPos
+  tst r19                            ; high byte zero?
+  breq flashCalcPosAndLength_8bit    ; yes, already 8-bit
+  ldi r18, 255                       ; clip size to 8 bit
+flashCalcPosAndLength_8bit:
+  cp r17, r18                        ; r18>r17?
+  brcc flashCalcPosAndLength_sizeOk  ; nope: jump
+  mov r18, r17                       ; clip r18 to size requested
+flashCalcPosAndLength_sizeOk:        ; r18=bytes to write
+  ldi xl, LOW(flashPageBuffer)       ; set X to pos within page buffer
   ldi xh, HIGH(flashPageBuffer)
   add xl, r24
-  adc xh, r24
-  sub xh, r24
+  adc xh, r25
   ret
 ; @end
 
@@ -245,17 +253,17 @@ flashEndPage_write:
 ; @routine flashReadPageIntoSram
 ;
 ; @param Z Address to read from (byte address as for LPM!)
-; @clobbers r16, r24, X, Z
+; @clobbers r16, r24, r25, X, Z
 
 flashReadPageIntoSram:
   ldi xl, LOW(flashPageBuffer)
   ldi xh, HIGH(flashPageBuffer)
   ldi r24, LOW(FLASH_PAGESIZE)
+  ldi r25, HIGH(FLASH_PAGESIZE)
 flashReadPageIntoSram_loop:
     lpm r16, Z+ 
     st X+, r16
-;    adiw ZH:ZL, 1
-    dec r24
+    sbiw r25:r24, 1
   brne flashReadPageIntoSram_loop
   ret
 ; @end