--- a/src/class.c
+++ b/src/class.c
@@ -1653,7 +1653,7 @@
     return classpath;
 }
 
-int filter(struct dirent *entry) {
+int filter(const struct dirent *entry) {
     int len = strlen(entry->d_name);
     char *ext = &entry->d_name[len-4];