diff --git a/sequential/linkedlist.hpp b/sequential/linkedlist.hpp
index 9713a89..96d4869 100644
--- a/sequential/linkedlist.hpp
+++ b/sequential/linkedlist.hpp
@@ -1,3 +1,4 @@
+#pragma once
 #include <memory>
 #include <stdexcept>
 
diff --git a/sequential/ringbuffer.hpp b/sequential/ringbuffer.hpp
index 0a663f1..6d835ea 100644
--- a/sequential/ringbuffer.hpp
+++ b/sequential/ringbuffer.hpp
@@ -1,3 +1,4 @@
+#pragma once
 #include "vector.hpp"
 
 template<class T>
diff --git a/sequential/vector.hpp b/sequential/vector.hpp
index fc851e6..2a19be2 100644
--- a/sequential/vector.hpp
+++ b/sequential/vector.hpp
@@ -1,3 +1,4 @@
+#pragma once
 #include <cstdlib>
 #include <stdexcept>
 
diff --git a/test/testutil.hpp b/test/testutil.hpp
index 2690320..6570323 100644
--- a/test/testutil.hpp
+++ b/test/testutil.hpp
@@ -1,3 +1,4 @@
+#pragma once
 #include <cstdio>
 #include <exception>
 #include <random>
diff --git a/tree/binarytree.hpp b/tree/binarytree.hpp
index 18a34a7..b74ec3c 100644
--- a/tree/binarytree.hpp
+++ b/tree/binarytree.hpp
@@ -1,3 +1,4 @@
+#pragma once
 #include <memory>
 
 namespace BinaryTree