diff --git a/include/linux/mfd/wm8994/core.h b/include/linux/mfd/wm8994/core.h
index f44bdb7..8eb1b75 100644
--- a/include/linux/mfd/wm8994/core.h
+++ b/include/linux/mfd/wm8994/core.h
@@ -15,6 +15,7 @@
 #ifndef __MFD_WM8994_CORE_H__
 #define __MFD_WM8994_CORE_H__
 
+#include <linux/mutex.h>
 #include <linux/interrupt.h>
 
 enum wm8994_type {