diff --git a/datastore_server/source/java/ch/systemsx/cisd/openbis/dss/generic/shared/utils/ImageUtil.java b/datastore_server/source/java/ch/systemsx/cisd/openbis/dss/generic/shared/utils/ImageUtil.java
index 3814dde5de713e4c52c75aeab04320c102636dbb..4190e0c2cc8b72d3c1d9db43578983a708a36570 100644
--- a/datastore_server/source/java/ch/systemsx/cisd/openbis/dss/generic/shared/utils/ImageUtil.java
+++ b/datastore_server/source/java/ch/systemsx/cisd/openbis/dss/generic/shared/utils/ImageUtil.java
@@ -475,7 +475,7 @@ public class ImageUtil
 
     }
 
-    static class ReaderAndFileHandler
+    private static class ReaderAndFileHandler
     {
         private IImageReader imageReader;
 
@@ -514,11 +514,6 @@ public class ImageUtil
             imageReader.close();
         }
 
-        @Override
-        protected void finalize() throws Throwable
-        {
-        }
-
         void setImageReader(IImageReader imageReader)
         {
             this.imageReader = imageReader;
diff --git a/screening/source/java/ch/systemsx/cisd/openbis/dss/etl/jython/v2/ImagingDataSetRegistrationTransaction.java b/screening/source/java/ch/systemsx/cisd/openbis/dss/etl/jython/v2/ImagingDataSetRegistrationTransaction.java
index a54595b0cf304399e5943710155f2bd9429854ec..745e96e1ea76891bceda3894230d4bc0bc3b5a38 100644
--- a/screening/source/java/ch/systemsx/cisd/openbis/dss/etl/jython/v2/ImagingDataSetRegistrationTransaction.java
+++ b/screening/source/java/ch/systemsx/cisd/openbis/dss/etl/jython/v2/ImagingDataSetRegistrationTransaction.java
@@ -127,6 +127,7 @@ public class ImagingDataSetRegistrationTransaction extends DataSetRegistrationTr
     {
         ImageUtil.closeSession(Thread.currentThread().getName());
         ImageUtil.setThreadLocalSessionId(null);
+        super.close();
     }
 
     public JythonPlateDatasetFactory getFactory()