diff --git a/lib/galaxy/tools/actions/__init__.py b/lib/galaxy/tools/actions/__init__.py
index 666a1c1709c..a51fe310de5 100644
--- a/lib/galaxy/tools/actions/__init__.py
+++ b/lib/galaxy/tools/actions/__init__.py
@@ -472,6 +472,15 @@ class DefaultToolAction( object ):
 
 
 def on_text_for_names( input_names ):
+    # input_names may contain duplicates... this is because the first value in
+    # multiple input dataset parameters will appear twice once as param_name
+    # and once as param_name1.
+    unique_names = []
+    for name in input_names:
+        if name not in unique_names:
+            unique_names.append( name )
+    input_names = unique_names
+
     # Build name for output datasets based on tool name and input names
     if len( input_names ) == 1:
         on_text = input_names[0]
diff --git a/test/unit/tools/test_actions.py b/test/unit/tools/test_actions.py
index 52ae7bc3416..710452ffb24 100644
--- a/test/unit/tools/test_actions.py
+++ b/test/unit/tools/test_actions.py
@@ -2,6 +2,7 @@ import unittest
 
 from galaxy import model
 from galaxy.tools.actions import DefaultToolAction
+from galaxy.tools.actions import on_text_for_names
 
 import tools_support
 
@@ -25,6 +26,19 @@ DATA_IN_LABEL_TOOL_CONTENTS = '''<tool id="test_tool" name="Test Tool">
 '''
 
 
+def test_on_text_for_names():
+    def assert_on_text_is( expected, *names ):
+        on_text = on_text_for_names( names )
+        assert on_text == expected, "Wrong on text value %s, expected %s" % ( on_text, expected )
+
+    assert_on_text_is( "data 1", "data 1" )
+    assert_on_text_is( "data 1 and data 2", "data 1", "data 2" )
+    assert_on_text_is( "data 1, data 2, and data 3", "data 1", "data 2", "data 3" )
+    assert_on_text_is( "data 1, data 2, and others", "data 1", "data 2", "data 3", "data 4" )
+
+    assert_on_text_is( "data 1 and data 2", "data 1", "data 1", "data 2" )
+
+
 class DefaultToolActionTestCase( unittest.TestCase, tools_support.UsesApp, tools_support.UsesTools ):
 
     def setUp( self ):