diff --git a/zealbooter/lib.h b/zealbooter/lib.h
index a3a19f56..50795a1d 100644
--- a/zealbooter/lib.h
+++ b/zealbooter/lib.h
@@ -1,3 +1,6 @@
+#ifndef __LIB_H__
+#define __LIB_H__
+
 #include <stdint.h>
 #include <memcpy.h>
 #include <print.h>
@@ -6,3 +9,5 @@ uint64_t div_roundup_u64(uint64_t a, uint64_t b);
 uint64_t align_up_u64(uint64_t a, uint64_t b);
 
 typedef char symbol[];
+
+#endif // __LIB_H__
diff --git a/zealbooter/memcpy.h b/zealbooter/memcpy.h
index 6945798f..c0600149 100644
--- a/zealbooter/memcpy.h
+++ b/zealbooter/memcpy.h
@@ -1,4 +1,8 @@
+#ifndef __MEMCPY_H__
+#define __MEMCPY_H__
 
 #include <stddef.h>
 
 void *memcpy(void *s1, const void *s2, size_t n);
+
+#endif // __MEMCPY_H__
diff --git a/zealbooter/print.h b/zealbooter/print.h
index b2b9bd34..e659b694 100644
--- a/zealbooter/print.h
+++ b/zealbooter/print.h
@@ -1,3 +1,6 @@
+#ifndef __PRINT_H__
+#define __PRINT_H__
 
 int printf(const char *format, ...);
 
+#endif // __PRINT_H__