diff --git a/Line.h b/Line.h
index 95cf75d..8ff77cb 100644
--- a/Line.h
+++ b/Line.h
@@ -1,4 +1,7 @@
-#pragma once
+#ifndef LINE_H
+#define LINE_H
+
+#include <cmath>  // For abs, sqrt
 
 #include "Point.h"
 
@@ -59,4 +62,5 @@ public:
 
         return (d * d) / (a * a + b * b);
     }
-};
\ No newline at end of file
+};
+#endif // LINE_H
\ No newline at end of file