diff --git a/lib/galaxy/model/__init__.py b/lib/galaxy/model/__init__.py
index 69be939b521e..9495b3a82401 100644
--- a/lib/galaxy/model/__init__.py
+++ b/lib/galaxy/model/__init__.py
@@ -1633,7 +1633,10 @@ def add_input_dataset(self, name, dataset=None, dataset_id=None):
 
     def add_output_dataset(self, name, dataset):
         joda = JobToOutputDatasetAssociation(name, dataset)
-        dataset.dataset.job = self
+        if dataset.dataset.job is None:
+            # Only set job if dataset doesn't already have associated job.
+            # database operation tools that make copies should not modify the job here.
+            dataset.dataset.job = self
         add_object_to_object_session(self, joda)
         self.output_datasets.append(joda)