diff --git a/invesalius/data/mask.py b/invesalius/data/mask.py
index 1fe79c1..9b3598a 100644
--- a/invesalius/data/mask.py
+++ b/invesalius/data/mask.py
@@ -480,4 +480,5 @@ class Mask():
                 self.save_history(index, orientation, matrix.copy(), cp_mask)
 
     def __del__(self):
+        del self.matrix
         os.remove(self.temp_file)
--
libgit2 0.21.2