diff --git a/rtd_phosphonetx/source/java/ch/systemsx/cisd/openbis/plugin/phosphonetx/client/web/client/application/ProteinViewer.java b/rtd_phosphonetx/source/java/ch/systemsx/cisd/openbis/plugin/phosphonetx/client/web/client/application/ProteinViewer.java
index 77d8904cde895a9e0198d32bf8972d4d0fca1f2f..f3eebdd9cce66cae55f848bbda6c342eef26c40d 100644
--- a/rtd_phosphonetx/source/java/ch/systemsx/cisd/openbis/plugin/phosphonetx/client/web/client/application/ProteinViewer.java
+++ b/rtd_phosphonetx/source/java/ch/systemsx/cisd/openbis/plugin/phosphonetx/client/web/client/application/ProteinViewer.java
@@ -312,7 +312,7 @@ public class ProteinViewer extends
         return observer;
     }
 
-    public static final class ProteinByExperimentCallback extends
+    private static final class ProteinByExperimentCallback extends
             AbstractAsyncCallback<ProteinByExperiment>
     {
         private final ProteinViewer viewer;