Index: stk500v2.c
--- stk500v2.c.orig
+++ stk500v2.c
@@ -350,6 +350,7 @@ static void stk500v2_jtag3_setup(PROGRAMMER * pgm)
 void stk500v2_teardown(PROGRAMMER * pgm)
 {
   free(pgm->cookie);
+  pgm->cookie = NULL;
 }
 
 static void stk500v2_jtagmkII_teardown(PROGRAMMER * pgm)
@@ -361,6 +362,7 @@ static void stk500v2_jtagmkII_teardown(PROGRAMMER * pg
   jtagmkII_teardown(pgm);
 
   free(mycookie);
+  pgm->cookie = NULL;
 }
 
 static void stk500v2_jtag3_teardown(PROGRAMMER * pgm)
@@ -1477,6 +1479,8 @@ static int stk500hv_initialize(PROGRAMMER * pgm, AVRPA
   }
   free(PDATA(pgm)->flash_pagecache);
   free(PDATA(pgm)->eeprom_pagecache);
+  PDATA(pgm)->flash_pagecache = NULL;
+  PDATA(pgm)->eeprom_pagecache = NULL;
   if ((PDATA(pgm)->flash_pagecache = malloc(PDATA(pgm)->flash_pagesize)) == NULL) {
     avrdude_message(MSG_INFO, "%s: stk500hv_initialize(): Out of memory\n",
 	    progname);
@@ -1486,6 +1490,7 @@ static int stk500hv_initialize(PROGRAMMER * pgm, AVRPA
     avrdude_message(MSG_INFO, "%s: stk500hv_initialize(): Out of memory\n",
 	    progname);
     free(PDATA(pgm)->flash_pagecache);
+    PDATA(pgm)->flash_pagecache = NULL;
     return -1;
   }
   PDATA(pgm)->flash_pageaddr = PDATA(pgm)->eeprom_pageaddr = (unsigned long)-1L;