diff --git a/lib/galaxy/tools/evaluation.py b/lib/galaxy/tools/evaluation.py
index da728abe101..f7adb8317e0 100644
--- a/lib/galaxy/tools/evaluation.py
+++ b/lib/galaxy/tools/evaluation.py
@@ -224,7 +224,7 @@ class ToolEvaluator( object ):
                     real_path = dataset.file_name
                     if real_path in input_dataset_paths:
                         wrapper_kwds[ "dataset_path" ] = input_dataset_paths[ real_path ]
-                identifier_key = param_dict[ "identifier_key" ].get( dataset, None )
+                identifier_key = identifier_key_dict.get(dataset, None)
                 if identifier_key:
                     element_identifier = param_dict.get(identifier_key, None)
                     if element_identifier:
@@ -256,7 +256,7 @@ class ToolEvaluator( object ):
         #       tools where the inputs don't even get passed through. These
         #       tools (e.g. UCSC) should really be handled in a special way.
         if self.tool.check_values:
-            param_dict[ "identifier_key" ] = dict((v, "%s|__identifier__" % k) for k, v in input_datasets.iteritems())  # allows lookup of identifier through HDA.
+            identifier_key_dict = dict((v, "%s|__identifier__" % k) for k, v in input_datasets.iteritems())  # allows lookup of identifier through HDA.
             self.__walk_inputs( self.tool.inputs, param_dict, wrap_input )
 
     def __populate_input_dataset_wrappers(self, param_dict, input_datasets, input_dataset_paths):