diff --git a/appl/ftp/ftp/cmds.c b/appl/ftp/ftp/cmds.c
index 52175d00b..c9aa3ffa3 100644
--- a/appl/ftp/ftp/cmds.c
+++ b/appl/ftp/ftp/cmds.c
@@ -468,14 +468,14 @@ mput(int argc, char **argv)
 	    if (mflag && confirm(argv[0], cp)) {
 		tp = cp;
 		if (mcase) {
-		    while (*tp && !islower(*tp)) {
+		    while (*tp && !islower((unsigned char)*tp)) {
 			tp++;
 		    }
 		    if (!*tp) {
 			tp = cp;
 			tp2 = tmpbuf;
 			while ((*tp2 = *tp) != '\0') {
-			    if (isupper(*tp2)) {
+			    if (isupper((unsigned char)*tp2)) {
 				*tp2 = 'a' + *tp2 - 'A';
 			    }
 			    tp++;
@@ -621,14 +621,14 @@ getit(int argc, char **argv, int restartit, char *mode)
 	if (loc && mcase) {
 		char *tp = argv[1], *tp2, tmpbuf[MaxPathLen];
 
-		while (*tp && !islower(*tp)) {
+		while (*tp && !islower((unsigned char)*tp)) {
 			tp++;
 		}
 		if (!*tp) {
 			tp = argv[2];
 			tp2 = tmpbuf;
 			while ((*tp2 = *tp) != '\0') {
-				if (isupper(*tp2)) {
+				if (isupper((unsigned char)*tp2)) {
 					*tp2 = 'a' + *tp2 - 'A';
 				}
 				tp++;
@@ -737,7 +737,7 @@ mget(int argc, char **argv)
 			tp = cp;
 			if (mcase) {
 				for (tp2 = tmpbuf; (ch = *tp++);)
-					*tp2++ = isupper(ch) ? tolower(ch) : ch;
+					*tp2++ = tolower(ch);
 				*tp2 = '\0';
 				tp = tmpbuf;
 			}
@@ -1831,7 +1831,7 @@ domap(char *name)
 				break;
 			case '[':
 LOOP:
-				if (*++cp2 == '$' && isdigit(*(cp2+1))) { 
+				if (*++cp2 == '$' && isdigit((unsigned char)*(cp2+1))) { 
 					if (*++cp2 == '0') {
 						char *cp3 = name;
 
@@ -1856,7 +1856,7 @@ LOOP:
 							cp2++;
 						}
 						else if (*cp2 == '$' &&
-   						        isdigit(*(cp2+1))) {
+   						        isdigit((unsigned char)*(cp2+1))) {
 							if (*++cp2 == '0') {
 							   char *cp3 = name;
 
@@ -1908,7 +1908,7 @@ LOOP:
 				}
 				break;
 			case '$':
-				if (isdigit(*(cp2 + 1))) {
+				if (isdigit((unsigned char)*(cp2 + 1))) {
 					if (*++cp2 == '0') {
 						char *cp3 = name;
 
diff --git a/appl/ftp/ftpd/ftpcmd.y b/appl/ftp/ftpd/ftpcmd.y
index 078e7b793..6d3ab883c 100644
--- a/appl/ftp/ftpd/ftpcmd.y
+++ b/appl/ftp/ftpd/ftpcmd.y
@@ -1238,9 +1238,9 @@ yylex(void)
 				cpos++;
 				return (SP);
 			}
-			if (isdigit(cbuf[cpos])) {
+			if (isdigit((unsigned char)cbuf[cpos])) {
 				cp = &cbuf[cpos];
-				while (isdigit(cbuf[++cpos]))
+				while (isdigit((unsigned char)cbuf[++cpos]))
 					;
 				c = cbuf[cpos];
 				cbuf[cpos] = '\0';
@@ -1253,9 +1253,9 @@ yylex(void)
 			goto dostr1;
 
 		case ARGS:
-			if (isdigit(cbuf[cpos])) {
+			if (isdigit((unsigned char)cbuf[cpos])) {
 				cp = &cbuf[cpos];
-				while (isdigit(cbuf[++cpos]))
+				while (isdigit((unsigned char)cbuf[++cpos]))
 					;
 				c = cbuf[cpos];
 				cbuf[cpos] = '\0';