diff --git a/helper_thread.h b/helper_thread.h
index d7df6c4d8..1c8167e83 100644
--- a/helper_thread.h
+++ b/helper_thread.h
@@ -1,6 +1,11 @@
 #ifndef FIO_HELPER_THREAD_H
 #define FIO_HELPER_THREAD_H
 
+#include <stdbool.h>
+
+struct fio_sem;
+struct sk_out;
+
 extern void helper_reset(void);
 extern void helper_do_stat(void);
 extern bool helper_should_exit(void);