diff --git a/include/geometry/PartsView.h b/include/geometry/PartsView.h
index 6cfb9bf4c6..e3881d9a3f 100644
--- a/include/geometry/PartsView.h
+++ b/include/geometry/PartsView.h
@@ -5,6 +5,7 @@
 #define GEOMETRY_PARTS_VIEW_H
 
 #include <vector>
+#include <cstddef> //For size_t.
 
 namespace cura
 {