diff --git a/avrdude/avr910.c b/avrdude/avr910.c
index 63bd6855..e0a97fac 100644
--- a/avrdude/avr910.c
+++ b/avrdude/avr910.c
@@ -46,7 +46,7 @@ static char has_auto_incr_addr;
 
 static int avr910_send(PROGRAMMER * pgm, char * buf, size_t len)
 {
-  return serial_send(pgm->fd, buf, len);
+  return serial_send(pgm->fd, (unsigned char *)buf, len);
 }
 
 
@@ -54,7 +54,7 @@ static int avr910_recv(PROGRAMMER * pgm, char * buf, size_t len)
 {
   int rv;
 
-  rv = serial_recv(pgm->fd, buf, len);
+  rv = serial_recv(pgm->fd, (unsigned char *)buf, len);
   if (rv < 0) {
     fprintf(stderr,
 	    "%s: avr910_recv(): programmer is not responding\n",
@@ -134,7 +134,7 @@ static int avr910_initialize(PROGRAMMER * pgm, AVRPART * p)
   char hw[2];
   char buf[10];
   char type;
-  unsigned char c;
+  char c;
   int dev_supported = 0;
   AVRPART * part;
 
@@ -232,7 +232,7 @@ static void avr910_enable(PROGRAMMER * pgm)
 static int avr910_cmd(PROGRAMMER * pgm, unsigned char cmd[4], 
                       unsigned char res[4])
 {
-  unsigned char buf[5];
+  char buf[5];
 
   /* FIXME: Insert version check here */
 
@@ -291,7 +291,7 @@ static void avr910_display(PROGRAMMER * pgm, char * p)
 
 static void avr910_set_addr(PROGRAMMER * pgm, unsigned long addr)
 {
-  unsigned char cmd[3];
+  char cmd[3];
 
   cmd[0] = 'A';
   cmd[1] = (addr >> 8) & 0xff;
@@ -305,7 +305,7 @@ static void avr910_set_addr(PROGRAMMER * pgm, unsigned long addr)
 static int avr910_write_byte(PROGRAMMER * pgm, AVRPART * p, AVRMEM * m,
                              unsigned long addr, unsigned char value)
 {
-  unsigned char cmd[2];
+  char cmd[2];
 
   if (strcmp(m->desc, "flash") == 0) {
     if (addr & 0x01) {
@@ -347,7 +347,7 @@ static int avr910_read_byte_flash(PROGRAMMER * pgm, AVRPART * p, AVRMEM * m,
     cached = 0;
   }
   else {
-    unsigned char buf[2];
+    char buf[2];
 
     avr910_set_addr(pgm, addr >> 1);
 
@@ -376,7 +376,7 @@ static int avr910_read_byte_eeprom(PROGRAMMER * pgm, AVRPART * p, AVRMEM * m,
 {
   avr910_set_addr(pgm, addr);
   avr910_send(pgm, "d", 1);
-  avr910_recv(pgm, value, 1);
+  avr910_recv(pgm, (char *)value, 1);
 
   return 0;
 }
@@ -401,7 +401,7 @@ static int avr910_paged_write_flash(PROGRAMMER * pgm, AVRPART * p, AVRMEM * m,
                                     int page_size, int n_bytes)
 {
   unsigned char cmd[] = {'c', 'C'};
-  unsigned char buf[2];
+  char buf[2];
   unsigned int addr = 0;
   unsigned int max_addr = n_bytes;
   unsigned int page_addr;
@@ -456,7 +456,7 @@ static int avr910_paged_write_flash(PROGRAMMER * pgm, AVRPART * p, AVRMEM * m,
 static int avr910_paged_write_eeprom(PROGRAMMER * pgm, AVRPART * p,
                                      AVRMEM * m, int page_size, int n_bytes)
 {
-  unsigned char cmd[2];
+  char cmd[2];
   unsigned int addr = 0;
   unsigned int max_addr = n_bytes;
 
@@ -500,11 +500,11 @@ static int avr910_paged_write(PROGRAMMER * pgm, AVRPART * p, AVRMEM * m,
 static int avr910_paged_load(PROGRAMMER * pgm, AVRPART * p, AVRMEM * m, 
                              int page_size, int n_bytes)
 {
-  unsigned char cmd;
+  char cmd;
   int rd_size;
   unsigned int addr = 0;
   unsigned int max_addr;
-  unsigned char buf[2];
+  char buf[2];
 
   if (strcmp(m->desc, "flash") == 0) {
     cmd = 'R';
@@ -532,7 +532,7 @@ static int avr910_paged_load(PROGRAMMER * pgm, AVRPART * p, AVRMEM * m,
       m->buf[addr*2+1] = buf[0];  /* MSB */
     }
     else {
-      avr910_recv(pgm, &m->buf[addr], 1);
+      avr910_recv(pgm, (char *)&m->buf[addr], 1);
     }
 
     addr++;
@@ -557,7 +557,7 @@ static int avr910_read_sig_bytes(PROGRAMMER * pgm, AVRPART * p, AVRMEM * m)
   }
 
   avr910_send(pgm, "s", 1);
-  avr910_recv(pgm, m->buf, 3);
+  avr910_recv(pgm, (char *)m->buf, 3);
 
   return 3;
 }
diff --git a/avrdude/butterfly.c b/avrdude/butterfly.c
index 97f99c14..358f660c 100644
--- a/avrdude/butterfly.c
+++ b/avrdude/butterfly.c
@@ -69,7 +69,7 @@ static int butterfly_send(PROGRAMMER * pgm, char * buf, size_t len)
 {
   no_show_func_info();
 
-  return serial_send(pgm->fd, buf, len);
+  return serial_send(pgm->fd, (unsigned char *)buf, len);
 }
 
 
@@ -79,7 +79,7 @@ static int butterfly_recv(PROGRAMMER * pgm, char * buf, size_t len)
 
   no_show_func_info();
 
-  rv = serial_recv(pgm->fd, buf, len);
+  rv = serial_recv(pgm->fd, (unsigned char *)buf, len);
   if (rv < 0) {
     fprintf(stderr,
 	    "%s: butterfly_recv(): programmer is not responding\n",
@@ -226,7 +226,7 @@ static int butterfly_initialize(PROGRAMMER * pgm, AVRPART * p)
   char hw[2];
   char buf[10];
   char type;
-  unsigned char c;
+  char c;
   int dev_supported = 0;
 
   no_show_func_info();
@@ -396,7 +396,7 @@ static void butterfly_display(PROGRAMMER * pgm, char * p)
 
 static void butterfly_set_addr(PROGRAMMER * pgm, unsigned long addr)
 {
-  unsigned char cmd[3];
+  char cmd[3];
 
   cmd[0] = 'A';
   cmd[1] = (addr >> 8) & 0xff;
@@ -411,7 +411,7 @@ static void butterfly_set_addr(PROGRAMMER * pgm, unsigned long addr)
 static int butterfly_write_byte(PROGRAMMER * pgm, AVRPART * p, AVRMEM * m,
                              unsigned long addr, unsigned char value)
 {
-  unsigned char cmd[6];
+  char cmd[6];
   int size;
 
   no_show_func_info();
@@ -460,7 +460,7 @@ static int butterfly_read_byte_flash(PROGRAMMER * pgm, AVRPART * p, AVRMEM * m,
     cached = 0;
   }
   else {
-    unsigned char buf[2];
+    char buf[2];
 
     butterfly_set_addr(pgm, addr >> 1);
 
@@ -489,7 +489,7 @@ static int butterfly_read_byte_eeprom(PROGRAMMER * pgm, AVRPART * p, AVRMEM * m,
 {
   butterfly_set_addr(pgm, addr);
   butterfly_send(pgm, "g\000\001E", 4);
-  butterfly_recv(pgm, value, 1);
+  butterfly_recv(pgm, (char *)value, 1);
   return 0;
 }
 
@@ -497,7 +497,7 @@ static int butterfly_read_byte_eeprom(PROGRAMMER * pgm, AVRPART * p, AVRMEM * m,
 static int butterfly_read_byte(PROGRAMMER * pgm, AVRPART * p, AVRMEM * m,
                             unsigned long addr, unsigned char * value)
 {
-  unsigned char cmd;
+  char cmd;
 
   no_show_func_info();
 
@@ -525,7 +525,7 @@ static int butterfly_read_byte(PROGRAMMER * pgm, AVRPART * p, AVRMEM * m,
     return -1;
 
   butterfly_send(pgm, &cmd, 1);
-  butterfly_recv(pgm, value, 1);
+  butterfly_recv(pgm, (char *)value, 1);
 
   return *value == '?'? -1: 0;
 }
@@ -537,7 +537,7 @@ static int butterfly_paged_write(PROGRAMMER * pgm, AVRPART * p, AVRMEM * m,
 {
   unsigned int addr = 0;
   unsigned int max_addr = n_bytes;
-  unsigned char *cmd;
+  char *cmd;
   unsigned int blocksize = buffersize;
 
   if (strcmp(m->desc, "flash") && strcmp(m->desc, "eeprom")) 
@@ -593,7 +593,7 @@ static int butterfly_paged_load(PROGRAMMER * pgm, AVRPART * p, AVRMEM * m,
     return -2;
 
   {		/* use buffered mode */
-    unsigned char cmd[4];
+    char cmd[4];
     int blocksize = buffersize;
 
     cmd[0] = 'g';
@@ -608,7 +608,7 @@ static int butterfly_paged_load(PROGRAMMER * pgm, AVRPART * p, AVRMEM * m,
       cmd[2] = blocksize & 0xff;
 
       butterfly_send(pgm, cmd, 4);
-      butterfly_recv(pgm, &m->buf[addr], blocksize);
+      butterfly_recv(pgm, (char *)&m->buf[addr], blocksize);
 
       addr += blocksize;
 
@@ -633,7 +633,7 @@ static int butterfly_read_sig_bytes(PROGRAMMER * pgm, AVRPART * p, AVRMEM * m)
   }
 
   butterfly_send(pgm, "s", 1);
-  butterfly_recv(pgm, m->buf, 3);
+  butterfly_recv(pgm, (char *)m->buf, 3);
   /* Returned signature has wrong order. */
   tmp = m->buf[2];
   m->buf[2] = m->buf[0];
diff --git a/avrdude/jtagmkII.c b/avrdude/jtagmkII.c
index ea7fe2a7..976f5439 100644
--- a/avrdude/jtagmkII.c
+++ b/avrdude/jtagmkII.c
@@ -295,7 +295,7 @@ static int jtagmkII_send(PROGRAMMER * pgm, unsigned char * data, size_t len)
   unsigned char *buf;
 
   if (verbose >= 3)
-    fprintf(stderr, "\n%s: jtagmkII_send(): sending %d bytes\n",
+    fprintf(stderr, "\n%s: jtagmkII_send(): sending %zd bytes\n",
 	    progname, len);
 
   if ((buf = malloc(len + 10)) == NULL)
@@ -627,7 +627,7 @@ static int jtagmkII_getsync(PROGRAMMER * pgm) {
 #undef FWVER
   if (verbose >= 2)
     fprintf(stderr,
-	    "%s: jtagmkII_getsync(): Using a %u-byte device descriptor\n",
+	    "%s: jtagmkII_getsync(): Using a %zu-byte device descriptor\n",
 	    progname, device_descriptor_length);
 
   /* Turn the ICE into JTAG mode */
@@ -1698,7 +1698,7 @@ static int jtagmkII_setparm(PROGRAMMER * pgm, unsigned char parm,
   memcpy(buf + 2, value, size);
   if (verbose >= 2)
     fprintf(stderr, "%s: jtagmkII_setparm(): "
-	    "Sending set parameter command (parm 0x%02x, %u bytes): ",
+	    "Sending set parameter command (parm 0x%02x, %zu bytes): ",
 	    progname, parm, size);
   jtagmkII_send(pgm, buf, size + 2);
 
diff --git a/avrdude/safemode.c b/avrdude/safemode.c
index 60f51fc7..5a20178b 100644
--- a/avrdude/safemode.c
+++ b/avrdude/safemode.c
@@ -66,7 +66,7 @@ int safemode_writefuse (unsigned char fuse, char * fusename, PROGRAMMER * pgm, A
 }
 
 /* Reads the fuses three times, checking that all readings are the same. This will ensure that the before values aren't in error! */
-int safemode_readfuses (char * lfuse, char * hfuse, char * efuse, PROGRAMMER * pgm, AVRPART * p, int verbose)  
+int safemode_readfuses (unsigned char * lfuse, unsigned char * hfuse, unsigned char * efuse, PROGRAMMER * pgm, AVRPART * p, int verbose)  
 {
 
   unsigned char value;
diff --git a/avrdude/safemode.h b/avrdude/safemode.h
index d854e237..7e5c4d83 100644
--- a/avrdude/safemode.h
+++ b/avrdude/safemode.h
@@ -28,7 +28,7 @@ amount of times before giving up */
 int safemode_writefuse (unsigned char fuse, char * fusename, PROGRAMMER * pgm, AVRPART * p, int tries, int verbose);
 
 /* Reads the fuses three times, checking that all readings are the same. This will ensure that the before values aren't in error! */
-int safemode_readfuses (char * lfuse, char * hfuse, char * efuse, PROGRAMMER * pgm, AVRPART * p, int verbose);
+int safemode_readfuses (unsigned char * lfuse, unsigned char * hfuse, unsigned char * efuse, PROGRAMMER * pgm, AVRPART * p, int verbose);
   
 /* This routine will store the current values pointed to by lfuse, hfuse, and efuse into an internal buffer in this routine
 when save is set to 1. When save is 0 (or not 1 really) it will copy the values from the internal buffer into the locations
diff --git a/avrdude/ser_posix.c b/avrdude/ser_posix.c
index 47f2ab5c..990476ff 100644
--- a/avrdude/ser_posix.c
+++ b/avrdude/ser_posix.c
@@ -167,14 +167,13 @@ static void ser_close(int fd)
 }
 
 
-static int ser_send(int fd, char * buf, size_t buflen)
+static int ser_send(int fd, unsigned char * buf, size_t buflen)
 {
   struct timeval timeout, to2;
   fd_set wfds;
   int nfds;
   int rc;
-
-  char * p = buf;
+  unsigned char * p = buf;
   size_t len = buflen;
 
   if (!len)
@@ -243,14 +242,13 @@ static int ser_send(int fd, char * buf, size_t buflen)
 }
 
 
-static int ser_recv(int fd, char * buf, size_t buflen)
+static int ser_recv(int fd, unsigned char * buf, size_t buflen)
 {
   struct timeval timeout, to2;
   fd_set rfds;
   int nfds;
   int rc;
-
-  char * p = buf;
+  unsigned char * p = buf;
   size_t len = 0;
 
   timeout.tv_sec  = serial_recv_timeout / 1000L;
diff --git a/avrdude/serial.h b/avrdude/serial.h
index 5dc8d745..5b557032 100644
--- a/avrdude/serial.h
+++ b/avrdude/serial.h
@@ -38,8 +38,8 @@ struct serial_device
   int (*setspeed)(int fd, long baud);
   void (*close)(int fd);
 
-  int (*send)(int fd, char * buf, size_t buflen);
-  int (*recv)(int fd, char * buf, size_t buflen);
+  int (*send)(int fd, unsigned char * buf, size_t buflen);
+  int (*recv)(int fd, unsigned char * buf, size_t buflen);
   int (*drain)(int fd, int display);
 };
 
diff --git a/avrdude/stk500.c b/avrdude/stk500.c
index 6e3532ad..b131a720 100644
--- a/avrdude/stk500.c
+++ b/avrdude/stk500.c
@@ -55,13 +55,13 @@ static int stk500_is_page_empty(unsigned int address, int page_size,
     const unsigned char *buf);
 
 
-static int stk500_send(PROGRAMMER * pgm, char * buf, size_t len)
+static int stk500_send(PROGRAMMER * pgm, unsigned char * buf, size_t len)
 {
   return serial_send(pgm->fd, buf, len);
 }
 
 
-static int stk500_recv(PROGRAMMER * pgm, char * buf, size_t len)
+static int stk500_recv(PROGRAMMER * pgm, unsigned char * buf, size_t len)
 {
   int rv;
 
diff --git a/avrdude/stk500v2.c b/avrdude/stk500v2.c
index eaf54095..b7d1cd2c 100644
--- a/avrdude/stk500v2.c
+++ b/avrdude/stk500v2.c
@@ -173,7 +173,7 @@ static int stk500v2_recv(PROGRAMMER * pgm, unsigned char msg[], size_t maxsize)
         if (curlen < maxsize) {
           msg[curlen] = c;
         } else {
-          fprintf(stderr, "%s: stk500v2_recv(): buffer too small, received %d byte into %d byte buffer\n",
+          fprintf(stderr, "%s: stk500v2_recv(): buffer too small, received %d byte into %zd byte buffer\n",
                   progname,curlen,maxsize);
           return -2;
         }
@@ -271,7 +271,7 @@ retry:
   return 0;
 }
 
-static int stk500v2_command(PROGRAMMER * pgm, char * buf, size_t len, size_t maxlen) {
+static int stk500v2_command(PROGRAMMER * pgm, unsigned char * buf, size_t len, size_t maxlen) {
   int i;
   int tries = 0;
   int status;