diff --git a/epan/dfilter/dfilter-macro.c b/epan/dfilter/dfilter-macro.c
index 6d9799b17b..9098d65162 100644
--- a/epan/dfilter/dfilter-macro.c
+++ b/epan/dfilter/dfilter-macro.c
@@ -221,7 +221,7 @@ gchar* dfilter_macro_apply(const gchar* text, guint depth, const gchar** error)
 					}
 					break;
 				} case NAME: {
-					if ( isalnum((int)c) || c == '_' ) {
+					if ( isalnum((guchar)c) || c == '_' ) {
 						g_string_append_c(name,c);
 					} else if ( c == ':') {
 						state = ARGS;
@@ -452,7 +452,7 @@ static gboolean macro_name_chk(void* r _U_, const char* in_name, unsigned name_l
 	guint i;
 
 	for (i=0; i < name_len; i++) {
-		if (!(in_name[i] == '_' || isalnum((int)in_name[i]) ) ) {
+		if (!(in_name[i] == '_' || isalnum((guchar)in_name[i]) ) ) {
 			*error = "invalid char in name";
 			return FALSE;
 		}
diff --git a/epan/strutil.c b/epan/strutil.c
index b7ab4d1d13..3f1b04db86 100644
--- a/epan/strutil.c
+++ b/epan/strutil.c
@@ -553,15 +553,15 @@ hex_str_to_bytes(const char *hex_str, GByteArray *bytes, gboolean force_separato
 gboolean
 uri_str_to_bytes(const char *uri_str, GByteArray *bytes) {
 	guint8		val;
-	const char	*p;
-	char		hex_digit[HEX_DIGIT_BUF_LEN];
+	const guchar	*p;
+	guchar		hex_digit[HEX_DIGIT_BUF_LEN];
 
 	g_byte_array_set_size(bytes, 0);
 	if (! uri_str) {
 		return FALSE;
 	}
 
-	p = uri_str;
+	p = (const guchar *)uri_str;
 
 	while (*p) {
 		if (! isascii(*p) || ! isprint(*p))
@@ -574,9 +574,9 @@ uri_str_to_bytes(const char *uri_str, GByteArray *bytes) {
 			if (*p == '\0') return FALSE;
 			hex_digit[1] = *p;
 			hex_digit[2] = '\0';
-			if (! isxdigit((int)hex_digit[0]) || ! isxdigit((int)hex_digit[1]))
+			if (! isxdigit(hex_digit[0]) || ! isxdigit(hex_digit[1]))
 				return FALSE;
-			val = (guint8) strtoul(hex_digit, NULL, 16);
+			val = (guint8) strtoul((char *)hex_digit, NULL, 16);
 			g_byte_array_append(bytes, &val, 1);
 		} else {
 			g_byte_array_append(bytes, (guint8 *) p, 1);
@@ -691,7 +691,7 @@ oid_str_to_bytes(const char *oid_str, GByteArray *bytes) {
   p = oid_str;
   dot = NULL;
   while (*p) {
-    if (!isdigit((int)*p) && (*p != '.')) return FALSE;
+    if (!isdigit((guchar)*p) && (*p != '.')) return FALSE;
     if (*p == '.') {
       if (p == oid_str) return FALSE;
       if (!*(p+1)) return FALSE;
@@ -707,7 +707,7 @@ oid_str_to_bytes(const char *oid_str, GByteArray *bytes) {
   subid0 = 0;	/* squelch GCC complaints */
   while (*p) {
     subid = 0;
-    while (isdigit((int)*p)) {
+    while (isdigit((guchar)*p)) {
       subid *= 10;
       subid += *p - '0';
       p++;
diff --git a/epan/uat.c b/epan/uat.c
index cd180f329d..44ec7a53c3 100644
--- a/epan/uat.c
+++ b/epan/uat.c
@@ -186,7 +186,7 @@ static void putfld(FILE* fp, void* rec, uat_field_t* f) {
 			for(i=0;i<fld_len;i++) {
 				char c = fld_ptr[i];
 				
-				if (c == '"' || c == '\\' || ! isprint((int)c) ) {
+				if (c == '"' || c == '\\' || ! isprint((guchar)c) ) {
 					fprintf(fp,"\\x%.2x",c);
 				} else {
 					putc(c,fp);
@@ -513,7 +513,7 @@ char* uat_unesc(const char* si, guint in_len, guint* len_p) {
 						char c1 = *(s+1);
 						char c0 = *(s+2);
 						
-						if (isxdigit((int)c1) && isxdigit((int)c0)) {
+						if (isxdigit((guchar)c1) && isxdigit((guchar)c0)) {
 							*(p++) = (xton(c1) * 0x10) + xton(c0);
 							s += 2;
 						} else {
diff --git a/fileset.c b/fileset.c
index 08201f7ee3..5405bd6c00 100644
--- a/fileset.c
+++ b/fileset.c
@@ -111,7 +111,7 @@ fileset_filename_match_pattern(const char *fname)
     while(minlen--) {
         baselen--;
 
-        if(!isdigit( (int) filename[baselen])) {
+        if(!isdigit( (guchar) filename[baselen])) {
             g_free(filename);
             return FALSE;
         }