diff --git a/include/common.h b/include/common.h
index b32728b9..7714dae6 100644
--- a/include/common.h
+++ b/include/common.h
@@ -1,3 +1,6 @@
+#ifndef COMMON_H
+#define COMMON_H
+
 typedef signed char s8;
 typedef signed short s16;
 typedef signed int s32;
@@ -15,4 +18,5 @@ typedef float f32;
 #define NULL 0
 
 double fabsf(double f);
-#pragma intrinsic(fabsf)
\ No newline at end of file
+#pragma intrinsic(fabsf)
+#endif