Unity 5 - submeshes don't work as before

In my project I’m using submeshes to place multiple materials on my mesh.
In Unity 5 they don’t seem to work as before.
I can generate the mesh without problems but if i want to apply the meshcollider to it, I’m getting this error:

“Failed getting triagles. Submesh 1 has no indices. UnityEngine.MeshCollider:set_sharedMesh(Mesh)”

In Unity 4.6 this wasn’t the case. Also it still works fine if you don’t use submeshes.
Any idea how to fix this?

Two potentially useful things for you.

One, see this question Unity5 - “Failed getting triangles”.

Two, a workaround might be to, for each material on the non-Collider Mesh you’re not otherwise generating a mesh for, set a trivial submesh. (e.g. see post 655 in the TerraVol thread).