diff --git a/fdrs_types.h b/fdrs_types.h
index 9687d01..6d5daf8 100644
--- a/fdrs_types.h
+++ b/fdrs_types.h
@@ -1,4 +1,5 @@
 #ifndef __FDRS_TYPES_H__
+#define __FDRS_TYPES_H__
 
 typedef struct __attribute__((packed)) DataReading {
     float data;