diff --git a/src/disasm.c b/src/disasm.c
index 33cc70db2..6f0c4eb3b 100644
--- a/src/disasm.c
+++ b/src/disasm.c
@@ -454,7 +454,7 @@ static int is_jumpable(int address) {
 
 // Format output for a label list r referenced by mnemonic m
 static void output_references(const char *m, char *r) {
-  disasm_out("; %c%s from ", toupper(*m), m + 1);
+  disasm_out("; %c%s from ", toupper(*m & 0xff), m + 1);
   for(char *s = r;;) {
     char *c = strchr(s + 1, ',');
 
@@ -513,7 +513,7 @@ static void lineout(const char *code, const char *comment,
         const char *mnestr = avr_opcodes[mne].opcode;
 
         disasm_out("%-*s ; %s\n", commentcol(), str_ccprintf("%s:", name),
-          str_ccprintf("%c%s from %s", toupper(*mnestr), mnestr + 1, reflist));
+          str_ccprintf("%c%s from %s", toupper(*mnestr & 0xff), mnestr + 1, reflist));
       } else {
         output_references(avr_opcodes[mne].opcode, reflist);
         if(comment)
diff --git a/src/strutil.c b/src/strutil.c
index be9108c5c..ad32d06c3 100644
--- a/src/strutil.c
+++ b/src/strutil.c
@@ -248,7 +248,7 @@ char *str_sprintf(const char *fmt, ...) {
 
   // Compute size
   va_start(ap, fmt);
-  size = vsnprintf(NULL, size, fmt, ap);
+  size = vsnprintf(NULL, 0, fmt, ap);
   va_end(ap);
 
   if(size < 0)
@@ -274,7 +274,7 @@ const char *str_ccprintf(const char *fmt, ...) {
 
   // Compute size
   va_start(ap, fmt);
-  size = vsnprintf(NULL, size, fmt, ap);
+  size = vsnprintf(NULL, 0, fmt, ap);
   va_end(ap);
 
   if(size < 0)
@@ -827,7 +827,7 @@ Str2data *str_todata(const char *s, int type, const AVRPART *part, const char *m
 
       // Parse suffixes: ULL, LL, UL, L ... UHH, HH
       for(char *p = end_ptr; *p; p++) {
-        switch(toupper(*p)) {
+        switch(toupper(*p & 0xff)) {
         case 'U':
           nu++;
           break;
@@ -847,7 +847,7 @@ Str2data *str_todata(const char *s, int type, const AVRPART *part, const char *m
 
       if(nx == 0 && nu < 2 && nl < 3 && nh < 3 && ns < 2) {     // Could be valid integer suffix
         // If U, then must be at start or end
-        if(nu == 0 || toupper(*end_ptr) == 'U' || toupper(str[arglen - 1]) == 'U') {
+        if(nu == 0 || toupper(*end_ptr & 0xff) == 'U' || toupper(str[arglen - 1] & 0xff) == 'U') {
           bool is_hex, is_bin;
           int ndigits;
 
@@ -940,7 +940,7 @@ Str2data *str_todata(const char *s, int type, const AVRPART *part, const char *m
 
   if(type & STR_DOUBLE) {       // Try double next, must have D suffix
     sd->d = strtod(str, &end_ptr);
-    if(end_ptr != str && toupper(*end_ptr) == 'D' && end_ptr[1] == 0) {
+    if(end_ptr != str && toupper(*end_ptr & 0xff) == 'D' && end_ptr[1] == 0) {
       sd->size = 8;
       sd->type = STR_DOUBLE;
       mmt_free(str);
@@ -951,7 +951,7 @@ Str2data *str_todata(const char *s, int type, const AVRPART *part, const char *m
   if(type & STR_FLOAT) {        // Try float next
     sd->size = 0;
     sd->f = strtof(str, &end_ptr);
-    if(end_ptr != str && toupper(*end_ptr) == 'F' && end_ptr[1] == 0)
+    if(end_ptr != str && toupper(*end_ptr & 0xff) == 'F' && end_ptr[1] == 0)
       sd->size = 4;
     // Do not accept valid mantissa-only floats that are integer rejects (eg, 078 or ULL overflows)
     if(end_ptr != str && *end_ptr == 0 && !is_mantissa_only(str))
diff --git a/src/term.c b/src/term.c
index b5a905b81..2a39d7951 100644
--- a/src/term.c
+++ b/src/term.c
@@ -258,7 +258,7 @@ static unsigned char *readbuf(const PROGRAMMER *pgm, const AVRPART *p, int argc,
   if(mi < 0 || mi >= Nmems)
     mi = 0;
 
-  const char *cmd = tolower(**argv) == 'r'? "read": str_casestarts(*argv, "di")? "disasm": "dump";
+  const char *cmd = tolower(**argv & 0xff) == 'r'? "read": str_casestarts(*argv, "di")? "disasm": "dump";
   int is_disasm = cmd[1] == 'i';
   int default_len = is_disasm? 32: 256;
 
@@ -1603,7 +1603,7 @@ static void printproperty(Cnfg *cc, int ii, Cfg_opts o) {
     if(o.verb > 1)
       term_out("# Mask 0x%02x of %s: %.*s\n", cc->t[ii].mask, cc[ii].memstr, cclen, ccom);
     else if(*cc[ii].t->ccomment)
-      term_out("# %c%.*s\n", toupper(*cc[ii].t->ccomment), cclen - 1, cc[ii].t->ccomment + 1);
+      term_out("# %c%.*s\n", toupper(*cc[ii].t->ccomment & 0xff), cclen - 1, cc[ii].t->ccomment + 1);
     else
       term_out("# %s\n", cc[ii].t->name);
   }
diff --git a/src/xbee.c b/src/xbee.c
index 4d77039af..f6ad446c2 100644
--- a/src/xbee.c
+++ b/src/xbee.c
@@ -230,9 +230,9 @@ static void xbeeStatsAdd(struct XBeeStaticticsSummary *summary, struct timeval c
 
 static void xbeeStatsSummarise(struct XBeeStaticticsSummary const *summary) {
   pmsg_notice("  Minimum response time: %lu.%06lu\n",
-    summary->minimum.tv_sec, (unsigned long) summary->minimum.tv_usec);
+    (unsigned long) summary->minimum.tv_sec, (unsigned long) summary->minimum.tv_usec);
   pmsg_notice("  Maximum response time: %lu.%06lu\n",
-    summary->maximum.tv_sec, (unsigned long) summary->maximum.tv_usec);
+    (unsigned long) summary->maximum.tv_sec, (unsigned long) summary->maximum.tv_usec);
 
   struct timeval average;
 
@@ -247,7 +247,8 @@ static void xbeeStatsSummarise(struct XBeeStaticticsSummary const *summary) {
   average.tv_sec += usecs/1000000;
   average.tv_usec = usecs%1000000;
 
-  pmsg_notice("  Average response time: %lu.%06lu\n", average.tv_sec, (unsigned long) average.tv_usec);
+  pmsg_notice("  Average response time: %lu.%06lu\n", (unsigned long) average.tv_sec,
+    (unsigned long) average.tv_usec);
 }
 
 static void XBeeBootSessionInit(struct XBeeBootSession *xbs) {