diff --git a/Sources/Core/Microsoft.StreamProcessing/Operators/SessionWindow/PartitionedSessionWindowPipe.cs b/Sources/Core/Microsoft.StreamProcessing/Operators/SessionWindow/PartitionedSessionWindowPipe.cs
index 1fdf85f03..13acf6c4f 100644
--- a/Sources/Core/Microsoft.StreamProcessing/Operators/SessionWindow/PartitionedSessionWindowPipe.cs
+++ b/Sources/Core/Microsoft.StreamProcessing/Operators/SessionWindow/PartitionedSessionWindowPipe.cs
@@ -249,15 +249,23 @@ public override int CurrentlyBufferedInputCount
 
         protected override void UpdatePointers()
         {
+            // Restore orderedKeysDictionary, as it is not Serialized/Deserialized
             int iter = FastDictionary<TKey, long>.IteratorStart;
             var temp = new List<Tuple<TKey, long, TPartitionKey>>();
             while (this.lastDataTimeDictionary.Iterate(ref iter))
             {
+                var partitionKey = this.getPartitionKey(this.lastDataTimeDictionary.entries[iter].key);
+
                 if (this.stateDictionary.entries[iter].value.Any())
                 {
                     temp.Add(Tuple.Create(
                         this.lastDataTimeDictionary.entries[iter].key,
-                        Math.Min(this.lastDataTimeDictionary.entries[iter].value + this.sessionTimeout, this.windowEndTimeDictionary.entries[iter].value), this.getPartitionKey(this.lastDataTimeDictionary.entries[iter].key)));
+                        Math.Min(this.lastDataTimeDictionary.entries[iter].value + this.sessionTimeout, this.windowEndTimeDictionary.entries[iter].value),
+                        partitionKey));
+                }
+                else if (!this.orderedKeysDictionary.ContainsKey(partitionKey))
+                {
+                    this.orderedKeysDictionary.Add(partitionKey, new LinkedList<TKey>());
                 }
             }
             foreach (var item in temp.OrderBy(o => o.Item2))
diff --git a/Sources/Test/SimpleTesting/Partitioned/PartitionedStreamCheckpointTests.cs b/Sources/Test/SimpleTesting/Partitioned/PartitionedStreamCheckpointTests.cs
new file mode 100644
index 000000000..8f94b9f63
--- /dev/null
+++ b/Sources/Test/SimpleTesting/Partitioned/PartitionedStreamCheckpointTests.cs
@@ -0,0 +1,101 @@
+// *********************************************************************
+// Copyright (c) Microsoft Corporation.  All rights reserved.
+// Licensed under the MIT License
+// *********************************************************************
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using System.Reactive.Linq;
+using System.Reactive.Subjects;
+using Microsoft.StreamProcessing;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+
+namespace SimpleTesting
+{
+    /* This test case verifies fix for
+     * Bug 944724: Exception in Trill SessionWindow when Partition (substreams) is used and restored from checkpoint
+     *
+     * Cause of the Bug:
+     *     The PartitionedSessionWindowPipe keeps multiple dictionary states.
+     *     One of the dictionary does not have a [DataMember] attribute, Because the value type is a LinkedList which does not support serialization.
+     *     On checkpoint and then Restore, this dictionary is re-created using other data members in UpdatePointers callback.
+     *     During this, the scenario of empty LinkedList value is missed and not restored.
+     *     When next data event appears for the partition, the partitionKey is indexed on the dictionary resulting in KeyNotFoundException
+    */
+    [TestClass]
+    public class PartitionedStreamCheckpointTests : TestWithConfigSettingsWithoutMemoryLeakDetection
+    {
+        [TestMethod, TestCategory("Gated")]
+        public void CheckpointPartitionedSessionWindow()
+        {
+            Config.DataBatchSize = 1;
+
+            var data = new PartitionedStreamEvent<int, double>[]
+            {
+                PartitionedStreamEvent.CreatePoint(0, 5, 1.0),
+                PartitionedStreamEvent.CreatePunctuation<int, double>(0, 8),
+                PartitionedStreamEvent.CreatePunctuation<int, double>(0, 11),
+                PartitionedStreamEvent.CreatePunctuation<int, double>(0, 14),
+                PartitionedStreamEvent.CreatePunctuation<int, double>(0, 17),
+                PartitionedStreamEvent.CreatePunctuation<int, double>(0, 21),
+                PartitionedStreamEvent.CreatePoint(0, 24, 1.0),
+                PartitionedStreamEvent.CreatePunctuation<int, double>(0, 100),
+            };
+
+            var expected = new PartitionedStreamEvent<int, double>[]
+            {
+                PartitionedStreamEvent.CreateStart(0, 5, 1.0),
+                PartitionedStreamEvent.CreatePunctuation<int, double>(0, 8),
+                PartitionedStreamEvent.CreateEnd(0, 9, 5, 1.0),
+                PartitionedStreamEvent.CreatePunctuation<int, double>(0, 11),
+                PartitionedStreamEvent.CreatePunctuation<int, double>(0, 14),
+                PartitionedStreamEvent.CreatePunctuation<int, double>(0, 17),
+                PartitionedStreamEvent.CreatePunctuation<int, double>(0, 21),
+                PartitionedStreamEvent.CreateStart(0, 24, 1.0),
+                PartitionedStreamEvent.CreateEnd(0, 28, 24, 1.0),
+                PartitionedStreamEvent.CreatePunctuation<int, double>(0, 100),
+            };
+
+            // This index represents the point when the checkpoint restore needs to happen to trigger the bug.
+            const int checkpointIndex = 6;
+
+            var subject = new Subject<PartitionedStreamEvent<int, double>>();
+            var output = new List<PartitionedStreamEvent<int, double>>();
+            var process = CreateQueryContainerForPartitionedStream(subject, output);
+
+            for (int i = 0; i < data.Length; i++)
+            {
+                if (i == checkpointIndex)
+                {
+                    using (var ms = new MemoryStream())
+                    {
+                        process.Checkpoint(ms);
+                        ms.Seek(0, SeekOrigin.Begin);
+
+                        subject = new Subject<PartitionedStreamEvent<int, double>>();
+                        process = CreateQueryContainerForPartitionedStream(subject, output, ms);
+                    }
+                }
+
+                subject.OnNext(data[i]);
+            }
+
+            Assert.IsTrue(expected.SequenceEqual(output));
+        }
+
+        private Process CreateQueryContainerForPartitionedStream(
+            Subject<PartitionedStreamEvent<int, double>> subject,
+            List<PartitionedStreamEvent<int, double>> output,
+            Stream stream = null)
+        {
+            var qc = new QueryContainer();
+            var input = qc.RegisterInput(subject);
+            var streamableOutput = input.SessionTimeoutWindow(4, 5).Sum(o => o);
+            var egress = qc.RegisterOutput(streamableOutput).ForEachAsync(o => output.Add(o));
+            var process = qc.Restore(stream);
+
+            return process;
+        }
+    }
+}