diff --git a/src/subtraction/subtraction.h b/src/subtraction/subtraction.h
index 8b13789..0ae67d9 100644
--- a/src/subtraction/subtraction.h
+++ b/src/subtraction/subtraction.h
@@ -1 +1,8 @@
+#ifndef subtraction_H
+#define subtraction_H
+
+int subtract(int a, int b);
+
+#endif
+