diff --git a/intern/cycles/blender/blender_mesh.cpp b/intern/cycles/blender/blender_mesh.cpp
index b4cca5f00f4..415337eb10b 100644
--- a/intern/cycles/blender/blender_mesh.cpp
+++ b/intern/cycles/blender/blender_mesh.cpp
@@ -64,6 +64,8 @@ inline void face_split_tri_indices(const int face_flag,
 		tri_b[2] = 1;
 	}
 	else /*if(face_flag & FACE_FLAG_DIVIDE_13)*/ {
+		assert(face_flag & FACE_FLAG_DIVIDE_13);
+
 		tri_a[0] = 0;
 		tri_a[1] = 1;
 		tri_a[2] = 2;