diff --git a/lib/galaxy/tools/__init__.py b/lib/galaxy/tools/__init__.py
index 8ab177ae6534..06035765aa03 100755
--- a/lib/galaxy/tools/__init__.py
+++ b/lib/galaxy/tools/__init__.py
@@ -2154,6 +2154,9 @@ def to_json(self, trans, kwd={}, job=None, workflow_mode=False):
         def jsonify(v):
             if isinstance(v, UnvalidatedValue):
                 v = v.value
+                while isinstance( v, UnvalidatedValue ):
+                    v = v.value
+                return v
 
             # check if value is numeric
             isnumber = False