diff --git a/src/tools/vector2d.hpp b/src/tools/vector2d.hpp
index 3ca2d585..f4aceff6 100644
--- a/src/tools/vector2d.hpp
+++ b/src/tools/vector2d.hpp
@@ -12,6 +12,7 @@
 // Tried using boost::multi_array, but it kept causing weird issues, so I decided to make my own.
 
 #include <vector>
+#include <cstddef>
 
 template<typename Type, typename Alloc = std::allocator<Type>> class vector2d {
 	friend class row_ref;