diff --git a/clients/tools/common.c b/clients/tools/common.c
index ac9c300afb..613bfb7b1a 100644
--- a/clients/tools/common.c
+++ b/clients/tools/common.c
@@ -1687,7 +1687,7 @@ tool_is_oid( const char *s )
 {
 	int		first = 1;
 
-	if ( !isdigit( s[ 0 ] ) ) {
+	if ( !isdigit( (unsigned char) s[ 0 ] ) ) {
 		return 0;
 	}
 
@@ -1700,7 +1700,7 @@ tool_is_oid( const char *s )
 			continue;
 		}
 
-		if ( !isdigit( s[ 0 ] ) ) {
+		if ( !isdigit( (unsigned char) s[ 0 ] ) ) {
 			return 0;
 		}
 
diff --git a/libraries/libldap/cyrus.c b/libraries/libldap/cyrus.c
index 296e633731..154fe80e57 100644
--- a/libraries/libldap/cyrus.c
+++ b/libraries/libldap/cyrus.c
@@ -1051,7 +1051,8 @@ int ldap_pvt_sasl_secprops(
 			if ( sprops[j].ival ) {
 				unsigned v;
 				char *next = NULL;
-				if ( !isdigit( props[i][sprops[j].key.bv_len] )) continue;
+				if ( !isdigit( (unsigned char)props[i][sprops[j].key.bv_len] ))
+					continue;
 				v = strtoul( &props[i][sprops[j].key.bv_len], &next, 10 );
 				if ( next == &props[i][sprops[j].key.bv_len] || next[0] != '\0' ) continue;
 				switch( sprops[j].ival ) {
diff --git a/libraries/libldap/url.c b/libraries/libldap/url.c
index c86e80e9ab..4c27ed33f2 100644
--- a/libraries/libldap/url.c
+++ b/libraries/libldap/url.c
@@ -346,7 +346,7 @@ hex_escape_len( const char *s, unsigned list )
 			
 		/* RFC 2396: unreserved alphanum */
 		default:
-			if ( !isalnum( s[0] ) ) {
+			if ( !isalnum( (unsigned char) s[0] ) ) {
 				len += 3;
 			} else {
 				len++;
@@ -411,7 +411,7 @@ hex_escape( char *buf, int len, const char *s, unsigned list )
 			
 		/* RFC 2396: unreserved alphanum */
 		default:
-			if ( !isalnum( s[i] ) ) {
+			if ( !isalnum( (unsigned char) s[i] ) ) {
 				escape = 1;
 			}
 			break;
diff --git a/libraries/liblutil/ldif.c b/libraries/liblutil/ldif.c
index 32e52d1ca7..defc1932d3 100644
--- a/libraries/liblutil/ldif.c
+++ b/libraries/liblutil/ldif.c
@@ -734,7 +734,7 @@ int ldif_is_not_printable(
 		ber_len_t i;
 
 		for ( i = 0; val[i]; i++ ) {
-			if ( !isascii( val[i] ) || !isprint( val[i] ) ) {
+			if ( !isascii( val[i] ) || !isprint( (unsigned char) val[i] ) ) {
 				return 1;
 			}
 		}
@@ -858,7 +858,7 @@ ldif_read_record(
 						}
 
 						ptr = line + STRLENOF("include:");
-						while (isspace(*ptr)) ptr++;
+						while (isspace((unsigned char) *ptr)) ptr++;
 						fp2 = ldif_open_url( ptr );
 						if ( fp2 ) {
 							LDIFFP *lnew = ber_memalloc( sizeof( LDIFFP ));
diff --git a/libraries/liblutil/utils.c b/libraries/liblutil/utils.c
index 77baee98c6..cb92e59f24 100644
--- a/libraries/liblutil/utils.c
+++ b/libraries/liblutil/utils.c
@@ -207,7 +207,7 @@ int lutil_parsetime( char *atm, struct lutil_tm *tm )
 		unsigned i, fracs;
 
 		/* Is the stamp reasonably long? */
-		for (i=0; isdigit(atm[i]); i++);
+		for (i=0; isdigit((unsigned char) atm[i]); i++);
 		if (i < sizeof("00000101000000")-1)
 			break;
 
@@ -247,7 +247,7 @@ int lutil_parsetime( char *atm, struct lutil_tm *tm )
 		if (tm->tm_sec < 0 || tm->tm_sec > 61) break;
 
 		/* Fractions of seconds */
-		for (i = 0, fracs = 0;isdigit(*ptr);) {
+		for (i = 0, fracs = 0; isdigit((unsigned char) *ptr); ) {
 			i*=10; i+= *ptr++ - '0';
 			fracs++;
 		}
diff --git a/servers/slapd/aclparse.c b/servers/slapd/aclparse.c
index 230dcdace2..96d8e4a88c 100644
--- a/servers/slapd/aclparse.c
+++ b/servers/slapd/aclparse.c
@@ -994,7 +994,7 @@ parse_acl(
 								< bdn->a_pat.bv_len;
 							exp = strchr( exp, '$' ) )
 						{
-							if ( isdigit( exp[ 1 ] ) ) {
+							if ( isdigit( (unsigned char) exp[ 1 ] ) ) {
 								gotit = 1;
 								break;
 							}
diff --git a/servers/slapd/back-bdb/config.c b/servers/slapd/back-bdb/config.c
index dd7feee8d1..34530f38f2 100644
--- a/servers/slapd/back-bdb/config.c
+++ b/servers/slapd/back-bdb/config.c
@@ -490,7 +490,7 @@ bdb_cf_gen(ConfigArgs *c)
 				struct berval bv, def = BER_BVC("default");
 				char *ptr;
 
-				for (ptr = c->line; !isspace( *ptr ); ptr++);
+				for (ptr = c->line; !isspace( (unsigned char) *ptr ); ptr++);
 
 				bv.bv_val = c->line;
 				bv.bv_len = ptr - bv.bv_val;
@@ -578,8 +578,8 @@ bdb_cf_gen(ConfigArgs *c)
 
 		if ( c->op == SLAP_CONFIG_ADD ) {
 			ptr += STRLENOF("dbconfig");
-			while (!isspace(*ptr)) ptr++;
-			while (isspace(*ptr)) ptr++;
+			while (!isspace((unsigned char)*ptr)) ptr++;
+			while (isspace((unsigned char)*ptr)) ptr++;
 		}
 
 		if ( bdb->bi_flags & BDB_IS_OPEN ) {
diff --git a/servers/slapd/back-ldap/config.c b/servers/slapd/back-ldap/config.c
index a00d820b64..3bda48fbea 100644
--- a/servers/slapd/back-ldap/config.c
+++ b/servers/slapd/back-ldap/config.c
@@ -353,7 +353,7 @@ ldap_back_cf_gen( ConfigArgs *c )
 
 			bindconf_unparse( &li->li_acl, &bv );
 
-			for ( i = 0; isspace( bv.bv_val[ i ] ); i++ )
+			for ( i = 0; isspace( (unsigned char) bv.bv_val[ i ] ); i++ )
 				/* count spaces */ ;
 
 			if ( i ) {
@@ -488,7 +488,7 @@ ldap_back_cf_gen( ConfigArgs *c )
 				bv.bv_len = ptr - bv.bv_val;
 
 			} else {
-				for ( i = 0; isspace( bc.bv_val[ i ] ); i++ )
+				for ( i = 0; isspace( (unsigned char) bc.bv_val[ i ] ); i++ )
 					/* count spaces */ ;
 
 				if ( i ) {
@@ -547,7 +547,7 @@ ldap_back_cf_gen( ConfigArgs *c )
 				return 1;
 			}
 
-			for ( i = 0; isspace( bv.bv_val[ i ] ); i++ )
+			for ( i = 0; isspace( (unsigned char) bv.bv_val[ i ] ); i++ )
 				/* count spaces */ ;
 
 			if ( i ) {
@@ -1157,7 +1157,7 @@ done_url:;
 
 	case LDAP_BACK_CFG_TIMEOUT:
 		for ( i = 1; i < c->argc; i++ ) {
-			if ( isdigit( c->argv[ i ][ 0 ] ) ) {
+			if ( isdigit( (unsigned char) c->argv[ i ][ 0 ] ) ) {
 				int		j;
 				unsigned	u;
 
diff --git a/servers/slapd/bconfig.c b/servers/slapd/bconfig.c
index 69c2da6664..b390fc990f 100644
--- a/servers/slapd/bconfig.c
+++ b/servers/slapd/bconfig.c
@@ -851,7 +851,7 @@ config_generic(ConfigArgs *c) {
 				AC_MEMCPY( abv.bv_val, ibuf, abv.bv_len );
 				/* Turn TAB / EOL into plain space */
 				for (src=bv.bv_val,dst=abv.bv_val+abv.bv_len; *src; src++) {
-					if (isspace(*src)) *dst++ = ' ';
+					if (isspace((unsigned char)*src)) *dst++ = ' ';
 					else *dst++ = *src;
 				}
 				*dst = '\0';
@@ -1416,8 +1416,8 @@ config_generic(ConfigArgs *c) {
 				char *ptr;
 				if ( c->op == SLAP_CONFIG_ADD ) {
 					ptr = c->line + STRLENOF("moduleload");
-					while (!isspace(*ptr)) ptr++;
-					while (isspace(*ptr)) ptr++;
+					while (!isspace((unsigned char) *ptr)) ptr++;
+					while (isspace((unsigned char) *ptr)) ptr++;
 				} else {
 					ptr = c->line;
 				}
@@ -2305,7 +2305,7 @@ config_loglevel(ConfigArgs *c) {
 	for( i=1; i < c->argc; i++ ) {
 		int	level;
 
-		if ( isdigit( c->argv[i][0] ) || c->argv[i][0] == '-' ) {
+		if ( isdigit((unsigned char)c->argv[i][0]) || c->argv[i][0] == '-' ) {
 			if( lutil_atoi( &level, c->argv[i] ) != 0 ) {
 				snprintf( c->msg, sizeof( c->msg ), "<%s> unable to parse level", c->argv[0] );
 				Debug( LDAP_DEBUG_ANY, "%s: %s \"%s\"\n",
diff --git a/servers/slapd/config.c b/servers/slapd/config.c
index 8e8558c053..2598291bc5 100644
--- a/servers/slapd/config.c
+++ b/servers/slapd/config.c
@@ -552,7 +552,7 @@ strtok_quote_ldif( char **line )
 	if ( !ptr || !*ptr )
 		return NULL;
 
-	while( isspace( *ptr )) ptr++;
+	while( isspace( (unsigned char) *ptr )) ptr++;
 
 	if ( *ptr == '"' ) {
 		inquote = 1;
@@ -563,7 +563,7 @@ strtok_quote_ldif( char **line )
 
 	for (;*ptr;ptr++) {
 		if ( *ptr == '"' ) {
-			if ( inquote && ( !ptr[1] || isspace(ptr[1]))) {
+			if ( inquote && ( !ptr[1] || isspace((unsigned char) ptr[1]))) {
 				*ptr++ = '\0';
 				break;
 			}
@@ -573,7 +573,7 @@ strtok_quote_ldif( char **line )
 		}
 		if ( inquote )
 			continue;
-		if ( isspace( *ptr )) {
+		if ( isspace( (unsigned char) *ptr )) {
 			*ptr++ = '\0';
 			break;
 		}
@@ -587,7 +587,7 @@ strtok_quote_ldif( char **line )
 	if ( !*ptr ) {
 		*line = NULL;
 	} else {
-		while ( isspace( *ptr )) ptr++;
+		while ( isspace( (unsigned char) *ptr )) ptr++;
 		*line = ptr;
 	}
 	return beg;
diff --git a/servers/slapd/main.c b/servers/slapd/main.c
index 46d24ba1db..119e24a955 100644
--- a/servers/slapd/main.c
+++ b/servers/slapd/main.c
@@ -244,7 +244,7 @@ parse_debug_level( const char *arg, int *levelp, char ***unknowns )
 {
 	int	level;
 
-	if ( arg != NULL && arg[ 0 ] != '-' && !isdigit( arg[ 0 ] ) )
+	if ( arg && arg[ 0 ] != '-' && !isdigit( (unsigned char) arg[ 0 ] ) )
 	{
 		int	i;
 		char	**levels;