diff --git a/model_server/base/roiset.py b/model_server/base/roiset.py
index 1993dc42e4c537074ef8cc7bd89259947f0f5278..2ce8477ec96107407e73249427fe9418e6a8cb1d 100644
--- a/model_server/base/roiset.py
+++ b/model_server/base/roiset.py
@@ -946,7 +946,7 @@ class RoiSet(object):
 
             # make a 3d patch
             if make_3d:
-                patch = patch3d
+                patch = patch3d.copy()
 
             # make a 2d patch, find optimal z-position determined by focus_metric function on each channel separately
             elif focus_metric is not None: