diff --git a/bl_types/bl_mesh.py b/bl_types/bl_mesh.py
index f564597..e79df18 100644
--- a/bl_types/bl_mesh.py
+++ b/bl_types/bl_mesh.py
@@ -159,7 +159,8 @@ class BlMesh(BlDatablock):
 
     def diff(self):
         return (self.bl_diff() or
-                len(self.pointer.vertices) != len(self.buffer['verts']))
+                len(self.pointer.vertices) != len(self.buffer['verts']) or 
+                len(self.pointer.materials) != len(self.buffer['materials']))
 
     def resolve_dependencies(self):
         deps = []