diff --git a/common/source/java/ch/systemsx/cisd/common/jython/v25/Jython25InterpreterFactory.java b/common/source/java/ch/systemsx/cisd/common/jython/v25/Jython25InterpreterFactory.java
index a8750976a494707ff6b63d9eb0cd7adec062a61b..12199f9f72c33c849097d565c8bbb9cd0b289dbd 100644
--- a/common/source/java/ch/systemsx/cisd/common/jython/v25/Jython25InterpreterFactory.java
+++ b/common/source/java/ch/systemsx/cisd/common/jython/v25/Jython25InterpreterFactory.java
@@ -153,7 +153,7 @@ public class Jython25InterpreterFactory implements IJythonInterpreterFactory
             try
             {
                 PyFunction function = interpreter.get(name, PyFunction.class);
-                return new Jython25Function(function);
+                return function == null ? null : new Jython25Function(function);
             } catch (Exception e)
             {
                 return null;