diff --git a/include/string.h b/include/string.h
index f4327a3..b906e15 100644
--- a/include/string.h
+++ b/include/string.h
@@ -1,3 +1,6 @@
+#ifndef __STRING_H
+#define __STRING_H
 
 #include <linux/string.h>
 
+#endif /* __STRING_H */