diff --git a/tests/progs/slapd-addel.c b/tests/progs/slapd-addel.c
index e99fbf00fe9bf1a3d49e70be3abda5112c9b97f5..80401e331e6c91e1f1abac44b2855fd067c26636 100644
--- a/tests/progs/slapd-addel.c
+++ b/tests/progs/slapd-addel.c
@@ -207,7 +207,8 @@ get_add_entry( char *filename, LDAPMod ***mods )
 			if ( !( value = strchr( line, ':' ))) break;
 
 			*value++ = '\0'; 
-			while ( *value && isspace( *value )) value++;
+			while ( *value && isspace( (unsigned char) *value ))
+				value++;
 
 			addmodifyop( mods, LDAP_MOD_ADD, line, value, strlen( value ));