diff --git a/src/ProductConstructionService/ProductConstructionService.DependencyFlow/PullRequestUpdater.cs b/src/ProductConstructionService/ProductConstructionService.DependencyFlow/PullRequestUpdater.cs
index 47d95d471..6c0eb56e6 100644
--- a/src/ProductConstructionService/ProductConstructionService.DependencyFlow/PullRequestUpdater.cs
+++ b/src/ProductConstructionService/ProductConstructionService.DependencyFlow/PullRequestUpdater.cs
@@ -1111,17 +1111,19 @@ private async Task UpdateCodeFlowPullRequestAsync(
         IRemote remote = await _remoteFactory.CreateRemoteAsync(subscription.TargetRepository);
         var build = await _sqlClient.GetBuildAsync(update.BuildId);
 
+        string? baseSourceSha= pullRequest.ContainedSubscriptions.FirstOrDefault(u => u.SubscriptionId.Equals(update.SubscriptionId))?.BaseSourceSha
+            ?? previousSourceSha;
         pullRequest.ContainedSubscriptions.RemoveAll(s => s.SubscriptionId.Equals(update.SubscriptionId));
         pullRequest.ContainedSubscriptions.Add(new SubscriptionPullRequestUpdate
         {
             SubscriptionId = update.SubscriptionId,
             BuildId = update.BuildId,
             SourceRepo = update.SourceRepo,
-            CommitSha = update.SourceSha
+            CommitSha = update.SourceSha,
+            BaseSourceSha = baseSourceSha,
         });
 
         pullRequest.RequiredUpdates = MergeExistingWithIncomingUpdates(pullRequest.RequiredUpdates, newDependencyUpdates);
-
         var title = _pullRequestBuilder.GenerateCodeFlowPRTitle(
             subscription.TargetBranch,
             pullRequest.ContainedSubscriptions.Select(s => s.SourceRepo).ToList());
@@ -1129,7 +1131,7 @@ private async Task UpdateCodeFlowPullRequestAsync(
         var description = _pullRequestBuilder.GenerateCodeFlowPRDescription(
             update,
             build,
-            previousSourceSha,
+            baseSourceSha,
             pullRequest.RequiredUpdates,
             prInfo?.Description,
             isForwardFlow: isForwardFlow);
@@ -1213,7 +1215,8 @@ private async Task<InProgressPullRequest> CreateCodeFlowPullRequestAsync(
                         SubscriptionId = update.SubscriptionId,
                         BuildId = update.BuildId,
                         SourceRepo = update.SourceRepo,
-                        CommitSha = update.SourceSha
+                        CommitSha = update.SourceSha,
+                        BaseSourceSha = previousSourceSha,
                     }
                 ],
                 RequiredUpdates = requiredUpdates,
diff --git a/src/ProductConstructionService/ProductConstructionService.DependencyFlow/SubscriptionPullRequestUpdate.cs b/src/ProductConstructionService/ProductConstructionService.DependencyFlow/SubscriptionPullRequestUpdate.cs
index 94211af7a..b84880ecd 100644
--- a/src/ProductConstructionService/ProductConstructionService.DependencyFlow/SubscriptionPullRequestUpdate.cs
+++ b/src/ProductConstructionService/ProductConstructionService.DependencyFlow/SubscriptionPullRequestUpdate.cs
@@ -20,4 +20,10 @@ public class SubscriptionPullRequestUpdate
 
     [DataMember]
     public string CommitSha { get; set; }
+
+    [DataMember]
+    /// <summary>
+    /// The earliest commit in the source repository from the changes contained in the current PR
+    /// </summary>
+    public string BaseSourceSha { get; set; }
 }
diff --git a/test/ProductConstructionService.DependencyFlow.Tests/PullRequestUpdaterTests.cs b/test/ProductConstructionService.DependencyFlow.Tests/PullRequestUpdaterTests.cs
index 6acaa2b1f..a1c36ecc7 100644
--- a/test/ProductConstructionService.DependencyFlow.Tests/PullRequestUpdaterTests.cs
+++ b/test/ProductConstructionService.DependencyFlow.Tests/PullRequestUpdaterTests.cs
@@ -51,7 +51,7 @@ protected override void RegisterServices(IServiceCollection services)
         services.AddSingleton(_forwardFlower.Object);
         services.AddSingleton(_gitClient.Object);
 
-        CodeFlowResult codeFlowRes = new CodeFlowResult(true, [], new NativePath(VmrPath), "aaa1234", []);
+        CodeFlowResult codeFlowRes = new CodeFlowResult(true, [], new NativePath(VmrPath), "base_codeflow_sha_123", []);
         _forwardFlower.SetReturnsDefault(Task.FromResult(codeFlowRes));
         _backFlower.SetReturnsDefault(Task.FromResult(codeFlowRes));
         _gitClient.SetReturnsDefault(Task.CompletedTask);
@@ -623,7 +623,8 @@ protected InProgressPullRequest CreatePullRequestState(
                     BuildId = forBuild.Id,
                     SubscriptionId = Subscription.Id,
                     SourceRepo = forBuild.GetRepository(),
-                    CommitSha = forBuild.Commit
+                    CommitSha = forBuild.Commit,
+                    BaseSourceSha = Subscription.SourceEnabled ? "base_codeflow_sha_123" : null,
                 }
             ],
             RequiredUpdates = forBuild.Assets
diff --git a/test/ProductConstructionService.DependencyFlow.Tests/UpdateAssetsForCodeFlowTests.cs b/test/ProductConstructionService.DependencyFlow.Tests/UpdateAssetsForCodeFlowTests.cs
index d7de106ee..a10b6520c 100644
--- a/test/ProductConstructionService.DependencyFlow.Tests/UpdateAssetsForCodeFlowTests.cs
+++ b/test/ProductConstructionService.DependencyFlow.Tests/UpdateAssetsForCodeFlowTests.cs
@@ -51,7 +51,8 @@ public async Task UpdateWithNoExistingState()
                     SubscriptionId = Subscription.Id,
                     BuildId = build.Id,
                     SourceRepo = build.GetRepository(),
-                    CommitSha = build.Commit
+                    CommitSha = build.Commit,
+                    BaseSourceSha = "base_codeflow_sha_123",
                 }
             ],
             RequiredUpdates = [],
@@ -178,7 +179,8 @@ public async Task UpdateWithManuallyMergedPrAndNewBuild()
                         SubscriptionId = Subscription.Id,
                         BuildId = build2.Id,
                         SourceRepo = build.GetRepository(),
-                        CommitSha = build2.Commit
+                        CommitSha = build2.Commit,
+                        BaseSourceSha = "base_codeflow_sha_123"
                     }
                 ],
                 RequiredUpdates = [],