diff --git a/invesalius/data/mask.py b/invesalius/data/mask.py
index 40df971..b36a6e9 100644
--- a/invesalius/data/mask.py
+++ b/invesalius/data/mask.py
@@ -386,4 +386,5 @@ class Mask():
     def __del__(self):
         if self.is_shown:
             self.history._config_undo_redo(False)
+        del self.matrix
         os.remove(self.temp_file)
--
libgit2 0.21.2