--- stk500-orig.c	2011-09-15 15:37:04.000000000 +0100
+++ stk500.c	2013-12-08 20:06:54.000000000 +0000
@@ -45,6 +45,8 @@
 
 #define STK500_XTAL 7372800U
 
+static unsigned char ext_addr_byte; /* Record ext-addr byte set in the target device (if used) */
+
 static int stk500_getparm(PROGRAMMER * pgm, unsigned parm, unsigned * value);
 static int stk500_setparm(PROGRAMMER * pgm, unsigned parm, unsigned value);
 static void stk500_print_parms1(PROGRAMMER * pgm, const char * p);
@@ -427,6 +429,7 @@
     n_extparms = 3;
 
   tries = 0;
+  ext_addr_byte = 0xff; /* Ensures it is programmed before first memory address */
 
  retry:
   tries++;
@@ -689,14 +692,30 @@
 }
 
 
-static int stk500_loadaddr(PROGRAMMER * pgm, unsigned int addr)
+static int stk500_loadaddr(PROGRAMMER * pgm, AVRMEM * mem, unsigned int addr)
 {
   unsigned char buf[16];
   int tries;
+  unsigned char ext_byte;
+  OPCODE * lext;
 
   tries = 0;
  retry:
   tries++;
+
+  /* To support flash > 64K words the correct Extended Address Byte is needed */
+  lext = mem->op[AVR_OP_LOAD_EXT_ADDR];
+  if (lext != NULL) {
+    ext_byte = (addr >> 16) & 0xff;
+    if (ext_byte != ext_addr_byte) {
+      /* Either this is the first addr load, or a 64K word boundary is crossed, so set the ext addr byte */
+      avr_set_bits(lext, buf);
+      avr_set_addr(lext, buf, addr);
+      stk500_cmd(pgm, buf, buf);
+      ext_addr_byte = ext_byte;
+    }
+  }
+
   buf[0] = Cmnd_STK_LOAD_ADDRESS;
   buf[1] = addr & 0xff;
   buf[2] = (addr >> 8) & 0xff;
@@ -822,7 +841,7 @@
     tries = 0;
   retry:
     tries++;
-    stk500_loadaddr(pgm, addr/a_div);
+    stk500_loadaddr(pgm, m, addr/a_div);
 
     /* build command block and avoid multiple send commands as it leads to a crash
         of the silabs usb serial driver on mac os x */
@@ -939,7 +958,7 @@
     tries = 0;
   retry:
     tries++;
-    stk500_loadaddr(pgm, addr/a_div);
+    stk500_loadaddr(pgm, m, addr/a_div);
     buf[0] = Cmnd_STK_READ_PAGE;
     buf[1] = (block_size >> 8) & 0xff;
     buf[2] = block_size & 0xff;