diff --git a/src/dhcp-common.c b/src/dhcp-common.c
index 84081ce..b4d255e 100644
--- a/src/dhcp-common.c
+++ b/src/dhcp-common.c
@@ -838,7 +838,7 @@ char *option_string(int prot, unsigned int opt, unsigned char *val, int opt_len,
 		for (i = 0, j = 0; i < opt_len && j < buf_len ; i++)
 		  {
 		    char c = val[i];
-		    if (isprint((int)c))
+		    if (isprint((unsigned char)c))
 		      buf[j++] = c;
 		  }
 #ifdef HAVE_DHCP6
@@ -852,7 +852,7 @@ char *option_string(int prot, unsigned int opt, unsigned char *val, int opt_len,
 		    for (k = i + 1; k < opt_len && k < l && j < buf_len ; k++)
 		     {
 		       char c = val[k];
-		       if (isprint((int)c))
+		       if (isprint((unsigned char)c))
 			 buf[j++] = c;
 		     }
 		    i = l;
@@ -873,7 +873,7 @@ char *option_string(int prot, unsigned int opt, unsigned char *val, int opt_len,
 		    for (k = 0; k < len && j < buf_len; k++)
 		      {
 		       char c = *p++;
-		       if (isprint((int)c))
+		       if (isprint((unsigned char)c))
 			 buf[j++] = c;
 		     }
 		    i += len +2;
diff --git a/src/dhcp.c b/src/dhcp.c
index 42d819f..e578391 100644
--- a/src/dhcp.c
+++ b/src/dhcp.c
@@ -916,14 +916,14 @@ void dhcp_read_ethers(void)
       
       lineno++;
       
-      while (strlen(buff) > 0 && isspace((int)buff[strlen(buff)-1]))
+      while (strlen(buff) > 0 && isspace((unsigned char)buff[strlen(buff)-1]))
 	buff[strlen(buff)-1] = 0;
       
       if ((*buff == '#') || (*buff == '+') || (*buff == 0))
 	continue;
       
-      for (ip = buff; *ip && !isspace((int)*ip); ip++);
-      for(; *ip && isspace((int)*ip); ip++)
+      for (ip = buff; *ip && !isspace((unsigned char)*ip); ip++);
+      for(; *ip && isspace((unsigned char)*ip); ip++)
 	*ip = 0;
       if (!*ip || parse_hex(buff, hwaddr, ETHER_ADDR_LEN, NULL, NULL) != ETHER_ADDR_LEN)
 	{
diff --git a/src/loop.c b/src/loop.c
index cd4855e..19bfae0 100644
--- a/src/loop.c
+++ b/src/loop.c
@@ -92,7 +92,7 @@ int detect_loop(char *query, int type)
     return 0;
 
   for (i = 0; i < 8; i++)
-    if (!isxdigit(query[i]))
+    if (!isxdigit((unsigned char)query[i]))
       return 0;
 
   uid = strtol(query, NULL, 16);
diff --git a/src/option.c b/src/option.c
index e4810fd..1090bca 100644
--- a/src/option.c
+++ b/src/option.c
@@ -2751,7 +2751,7 @@ static int one_opt(int option, char *arg, char *errstr, char *gen_err, int comma
 		ret_err(gen_err);
 	      
 	      for (p = arg; *p; p++)
-		if (!isxdigit((int)*p))
+		if (!isxdigit((unsigned char)*p))
 		  ret_err(gen_err);
 	      
 	      set_option_bool(OPT_UMBRELLA_DEVID);
@@ -4836,7 +4836,7 @@ err:
 	    new->target = target;
 	    new->ttl = ttl;
 
-	    for (arg += arglen+1; *arg && isspace(*arg); arg++);
+	    for (arg += arglen+1; *arg && isspace((unsigned char)*arg); arg++);
 	  }
       
 	break;
@@ -5227,7 +5227,7 @@ err:
 	unhide_metas(keyhex);
 	/* 4034: "Whitespace is allowed within digits" */
 	for (cp = keyhex; *cp; )
-	  if (isspace(*cp))
+	  if (isspace((unsigned char)*cp))
 	    for (cp1 = cp; *cp1; cp1++)
 	      *cp1 = *(cp1+1);
 	  else
@@ -5315,7 +5315,7 @@ static void read_file(char *file, FILE *f, int hard_opt, int from_script)
 	      memmove(p, p+1, strlen(p+1)+1);
 	    }
 
-	  if (isspace(*p))
+	  if (isspace((unsigned char)*p))
 	    {
 	      *p = ' ';
 	      white = 1;
diff --git a/src/rfc1035.c b/src/rfc1035.c
index 5c0df56..1693253 100644
--- a/src/rfc1035.c
+++ b/src/rfc1035.c
@@ -519,7 +519,7 @@ static int print_txt(struct dns_header *header, const size_t qlen, char *name,
       /* make counted string zero-term and sanitise */
       for (i = 0; i < len; i++)
 	{
-	  if (!isprint((int)*(p3+1)))
+	  if (!isprint((unsigned char)*(p3+1)))
 	    break;
 	  *p3 = *(p3+1);
 	  p3++;
diff --git a/src/rfc2131.c b/src/rfc2131.c
index 17e97b5..5190982 100644
--- a/src/rfc2131.c
+++ b/src/rfc2131.c
@@ -1678,7 +1678,7 @@ static int sanitise(unsigned char *opt, char *buf)
   for (i = option_len(opt); i > 0; i--)
     {
       char c = *p++;
-      if (isprint((int)c))
+      if (isprint((unsigned char)c))
 	*buf++ = c;
     }
   *buf = 0; /* add terminator */
diff --git a/src/tftp.c b/src/tftp.c
index 0861f37..8e1dc4a 100644
--- a/src/tftp.c
+++ b/src/tftp.c
@@ -405,7 +405,7 @@ void tftp_request(struct listener *listen, time_t now)
 	if (*p == '\\')
 	  *p = '/';
 	else if (option_bool(OPT_TFTP_LC))
-	  *p = tolower(*p);
+	  *p = tolower((unsigned char)*p);
 		
       strcpy(daemon->namebuff, "/");
       if (prefix)