diff --git a/src/exit_code.h b/src/exit_code.h
index d582963..17fee87 100644
--- a/src/exit_code.h
+++ b/src/exit_code.h
@@ -1,3 +1,6 @@
+#ifndef EXIT_CODE_H
+#define EXIT_CODE_H
+
 typedef enum {
     EXIT_OK = 0,
     ERR_ARGUMENT = 1,
@@ -7,3 +10,5 @@ typedef enum {
     ERR_MEMORY = 5,
     ERR_QUERY = 6,
 } exit_code;
+
+#endif