diff --git a/src/gbemu/cpu.h b/src/gbemu/cpu.h
index 2da6a8c..eeff950 100644
--- a/src/gbemu/cpu.h
+++ b/src/gbemu/cpu.h
@@ -5,6 +5,9 @@
  * Last Modified: 11-17-2015
  */
 
+#ifndef GB_CPU_H
+#define GB_CPU_H
+
 #include <stdint.h>
 
 #define LR35902_FLAG_BIT_C 4
@@ -115,3 +118,5 @@ void lr35902_set_reg_8(struct lr35902_state *cpu,
                        uint8_t val);
 
 void lr35902_cycle(struct lr35902_state *cpu);
+
+#endif