diff --git a/src/user/user_mesh.cc b/src/user/user_mesh.cc
index 21f05cbe..a1c30cbe 100644
--- a/src/user/user_mesh.cc
+++ b/src/user/user_mesh.cc
@@ -62,7 +62,6 @@
 #include "user/user_objects.h"
 #include "user/user_resource.h"
 #include "user/user_util.h"
-#include <tiny_obj_loader.h>
 
 extern "C" {
 #include "qhull_ra.h"
@@ -395,7 +394,7 @@ void mjCMesh::CacheMesh(mjCCache* cache, const mjResource* resource,
       + (sizeof(int) * vertex_index_.size())
       + (sizeof(int) * normal_index_.size())
       + (sizeof(int) * texcoord_index_.size())
-      + (sizeof(unsigned char) * num_face_vertices_.size());
+      + (sizeof(face_vertices_type) * num_face_vertices_.size());
 
   std::shared_ptr<const void> cached_data(mesh, +[](const void* data) {
     const mjCMesh* mesh = static_cast<const mjCMesh*>(data);
diff --git a/src/user/user_objects.h b/src/user/user_objects.h
index 8d853946..073182b3 100644
--- a/src/user/user_objects.h
+++ b/src/user/user_objects.h
@@ -31,6 +31,10 @@
 #include <mujoco/mjspec.h>
 #include "user/user_cache.h"
 #include "user/user_util.h"
+#include <tiny_obj_loader.h>
+
+using face_vertices_type =
+    decltype(tinyobj::mesh_t::num_face_vertices)::value_type;
 
 // forward declarations of all mjC/X classes
 class mjCError;
@@ -1010,7 +1014,7 @@ class mjCMesh: public mjCMesh_, private mjsMesh {
   std::vector<int> vertex_index_;
   std::vector<int> normal_index_;
   std::vector<int> texcoord_index_;
-  std::vector<unsigned char> num_face_vertices_;
+  std::vector<face_vertices_type> num_face_vertices_;
 
   // compute the volume and center-of-mass of the mesh given the face center
   void ComputeVolume(double CoM[3], mjtGeomInertia gtype, const double facecen[3]);