diff --git a/__init__.py b/__init__.py
index bbbd4c9..582003f 100644
--- a/__init__.py
+++ b/__init__.py
@@ -380,8 +380,9 @@ _create_vertices.argtypes = (
     ctypes.c_void_p) # meshes
 
 def create_vertices(format, nvertices, vertices, indices, meshes):
+    assert len(meshes) % 2 == 0
     return _create_vertices(format,
-        nvertices, _ubyte_addr(vertices), len(indices), _ushort_addr(indices), len(meshes), _uint_addr(meshes))
+        nvertices, _ubyte_addr(vertices), len(indices), _ushort_addr(indices), len(meshes) // 2, _uint_addr(meshes))
 
 create_batch = _engine.rk_create_batch
 create_batch.restype = _handle
diff --git a/cpp/render.hpp b/cpp/render.hpp
index efdde96..4629b98 100644
--- a/cpp/render.hpp
+++ b/cpp/render.hpp
@@ -72,12 +72,9 @@ enum : rk_ubyte { RK_INSTANCE_FLAGS_SPAWNED_VISIBLE = RK_INSTANCE_FLAG_SPAWNED |
 
 enum : rk_uint { RK_BATCH_MAX_SIZE = 65536 };
 
-union rk_mesh {
-    rk_uint packed;
-    struct {
-        rk_ushort base_index;
-        rk_ushort ntriangles;
-    };
+struct rk_mesh {
+    rk_uint base_index;
+    rk_uint ntriangles;
 };
 
 RK_EXPORT void rk_render_initialize(