diff --git a/static/scripts/galaxy.workflow_editor.canvas.js b/static/scripts/galaxy.workflow_editor.canvas.js
index 83a1397d8e0..9414eb090af 100644
--- a/static/scripts/galaxy.workflow_editor.canvas.js
+++ b/static/scripts/galaxy.workflow_editor.canvas.js
@@ -302,19 +302,12 @@ var BaseInputTerminal = Terminal.extend( {
             inputFilled = false;
         } else {
             if( this.multiple ) {
-                if( ! this.connected() ) {
-                    inputFilled = false;
+                if(this._collectionAttached()) {
+                    // Can only attach one collection to multiple input
+                    // data parameter.
+                    inputsFilled = true;
                 } else {
-                    var firstOutput = this.connectors[ 0 ].handle1;
-                    if( ! firstOutput ){
-                        inputFilled = false;
-                    } else {
-                        if( firstOutput.isDataCollectionInput || firstOutput.isMappedOver() || firstOutput.datatypes.indexOf( "input_collection" ) > 0 ) {
-                            inputFilled = true;
-                        } else {
-                            inputFilled = false;
-                        }
-                    }
+                    inputFilled = false;
                 }
             } else {
                 inputFilled = true;
@@ -322,6 +315,22 @@ var BaseInputTerminal = Terminal.extend( {
         }
         return inputFilled;
     },
+    _collectionAttached: function( ) {
+        if( ! this.connected() ) {
+            return false;
+        } else {
+            var firstOutput = this.connectors[ 0 ].handle1;
+            if( ! firstOutput ){
+                return false;
+            } else {
+                if( firstOutput.isDataCollectionInput || firstOutput.isMappedOver() || firstOutput.datatypes.indexOf( "input_collection" ) > 0 ) {
+                    return true;
+                } else {
+                    return false;
+                }
+            }
+        }
+    },
     _mappingConstraints: function( ) {
         // If this is a connected terminal, return list of collection types
         // other terminals connected to node are constraining mapping to.
@@ -407,7 +416,9 @@ var InputTerminal = BaseInputTerminal.extend( {
         var thisMapOver = this.mapOver();
         if( otherCollectionType.isCollection ) {
             if( this.multiple ) {
-                if( this.connected() ) {
+                if( this.connected() && ! this._collectionAttached() ) {
+                    // if single inputs attached, cannot also attach a
+                    // collection (yet...)
                     return false;
                 }
                 if( otherCollectionType.rank == 1 ) {
diff --git a/test/qunit/tests/workflow_editor_tests.js b/test/qunit/tests/workflow_editor_tests.js
index 37f32e0bed2..f30b8f71829 100644
--- a/test/qunit/tests/workflow_editor_tests.js
+++ b/test/qunit/tests/workflow_editor_tests.js
@@ -91,7 +91,9 @@ define([
         },
         test_accept: function( other ) {
             other = other || { node: {}, datatypes: [ "txt" ] };
-            other.mapOver = function() { return NULL_COLLECTION_TYPE_DESCRIPTION; };
+            if( ! other.mapOver ) {
+                other.mapOver = function() { return NULL_COLLECTION_TYPE_DESCRIPTION; };
+            }
             return this.input_terminal.canAccept( other );
         },
         pja_change_datatype_node: function( output_name, newtype ) {
@@ -230,6 +232,22 @@ define([
         ok( self.test_accept() );
     } );
 
+    test( "can accept list collection for empty multiple inputs", function() {
+        var other = { node: {}, datatypes: [ "tabular" ], mapOver: function() { return new CollectionTypeDescription( "list" ) } };
+        var self = this;
+        this.multiple();
+        ok( self.test_accept( other ) );
+    } );
+
+    test( "cannot accept list collection for multiple input if collection already connected", function() {
+        var other = { node: {}, datatypes: [ "tabular" ], mapOver: function() { return new CollectionTypeDescription( "list" ) } };
+        var self = this;
+        this.multiple();
+        this.with_test_connector( function() {
+            ok( ! self.test_accept( other ) );
+        } );
+    } );
+
     module( "Connector test", {
 
     } );
@@ -483,6 +501,17 @@ define([
 
             return c;
         },
+        connectAttachedMultiInputTerminal: function( inputType, outputType ) {
+            this.view.addDataInput( { name: "TestName", extensions: [ inputType ], multiple: true } );
+            var terminal = this.view.node.input_terminals[ "TestName" ];
+
+            var outputTerminal = new OutputTerminal( { name: "TestOuptut", datatypes: [ "txt" ] } );
+            outputTerminal.node = { markChanged: function() {}, post_job_actions: [], hasMappedOverInputTerminals: function() { return false; }, hasConnectedOutputTerminals: function() { return true; } };
+            outputTerminal.terminalMapping = { disableMapOver: function() {}, mapOver: new CollectionTypeDescription( "list" ) };
+            var c = new Connector( outputTerminal, terminal );
+
+            return c;
+        },
         connectAttachedMappedOutput: function( ) {
             this.view.addDataInput( { name: "TestName", extensions: [ "txt" ], input_type: "dataset_collection" } );
             var terminal = this.view.node.input_terminals[ "TestName" ];
@@ -530,6 +559,14 @@ define([
         ok( connector.handle2 === terminal );
     } );
 
+    test( "replacing terminal on data multiple input update preserves collection connections", function() {
+        var connector = this.connectAttachedMultiInputTerminal( "txt", "txt" );
+        var connector_destroy_spy = sinon.spy( connector, "destroy" );
+        var newElement = $("<div class='inputs'></div>");
+        this.view.addDataInput( { name: "TestName", extensions: ["txt"], multiple: true }, newElement );
+        ok( ! connector_destroy_spy.called );
+    } );
+
     test( "replacing mapped terminal on data collection input update preserves connections", function() {
         var connector = this.connectAttachedMappedOutput();
         var newElement = $("<div class='inputs'></div>");
@@ -922,12 +959,11 @@ define([
         this.verifyAttachable( inputTerminal1, "list" );
     } );
 
-    test( "connected multiple input cannot be connected to collections", function() {
+    test( "multiple input attachable by collections", function() {
         var inputTerminal1 = this.newInputTerminal( null, { multiple: true } );
         var connectedInput1 = this.addConnectedInput( inputTerminal1 );
         this.addConnectedOutput( connectedInput1 );
-        // Normally could do this reduction, but cannot because input already connected.
-        this.verifyNotAttachable( connectedInput1, "list" );
+        this.verifyAttachable( inputTerminal1, "list" );
     } );
 
     test( "unconnected multiple inputs cannot be connected to rank > 1 collections (yet...)", function() {