diff --git a/geometry/graham_scan_algorithm.cpp b/geometry/graham_scan_algorithm.cpp
index 44a8b300f..80d5e3799 100644
--- a/geometry/graham_scan_algorithm.cpp
+++ b/geometry/graham_scan_algorithm.cpp
@@ -37,7 +37,7 @@
 #include <iostream>                       /// for IO Operations
 #include <cassert>                        /// for std::assert
 #include <vector>                         /// for std::vector
-#include "./graham_scan_functions.h"      /// for all the functions used
+#include "./graham_scan_functions.hpp"    /// for all the functions used
 
 /*******************************************************************************
  * @brief Self-test implementations