diff --git a/Microsoft.Azure.Cosmos/src/ChangeFeedProcessor/LeaseManagement/DocumentServiceLeaseManagerCosmos.cs b/Microsoft.Azure.Cosmos/src/ChangeFeedProcessor/LeaseManagement/DocumentServiceLeaseManagerCosmos.cs
index 0f343a7732..6ad742cf07 100644
--- a/Microsoft.Azure.Cosmos/src/ChangeFeedProcessor/LeaseManagement/DocumentServiceLeaseManagerCosmos.cs
+++ b/Microsoft.Azure.Cosmos/src/ChangeFeedProcessor/LeaseManagement/DocumentServiceLeaseManagerCosmos.cs
@@ -128,7 +128,11 @@ public override Task<DocumentServiceLease> CreateLeaseIfNotExistAsync(
                 Mode = this.GetChangeFeedMode()
             };
 
-            this.requestOptionsFactory.AddPartitionKeyIfNeeded((string pk) => documentServiceLease.LeasePartitionKey = pk, Guid.NewGuid().ToString());
+            // Use the lease document id as the partition-key value so that retries / concurrent
+            // creates for the same lease resolve to the same (id, partitionKey) tuple. This lets the
+            // Cosmos per-partition-key id-uniqueness check turn duplicates into a 409 Conflict
+            // instead of silently persisting cross-partition-key duplicates.
+            this.requestOptionsFactory.AddPartitionKeyIfNeeded((string pk) => documentServiceLease.LeasePartitionKey = pk, leaseDocId);
 
             return this.TryCreateDocumentServiceLeaseAsync(documentServiceLease);
         }
@@ -153,7 +157,11 @@ public override Task<DocumentServiceLease> CreateLeaseIfNotExistAsync(
                 Mode = this.GetChangeFeedMode()
             };
 
-            this.requestOptionsFactory.AddPartitionKeyIfNeeded((string pk) => documentServiceLease.LeasePartitionKey = pk, Guid.NewGuid().ToString());
+            // Use the lease document id as the partition-key value so that retries / concurrent
+            // creates for the same lease resolve to the same (id, partitionKey) tuple. This lets the
+            // Cosmos per-partition-key id-uniqueness check turn duplicates into a 409 Conflict
+            // instead of silently persisting cross-partition-key duplicates.
+            this.requestOptionsFactory.AddPartitionKeyIfNeeded((string pk) => documentServiceLease.LeasePartitionKey = pk, leaseDocId);
 
             return this.TryCreateDocumentServiceLeaseAsync(documentServiceLease);
         }
diff --git a/Microsoft.Azure.Cosmos/tests/Microsoft.Azure.Cosmos.Tests/ChangeFeed/DocumentServiceLeaseManagerCosmosTests.cs b/Microsoft.Azure.Cosmos/tests/Microsoft.Azure.Cosmos.Tests/ChangeFeed/DocumentServiceLeaseManagerCosmosTests.cs
index d93167e639..86f4a626cb 100644
--- a/Microsoft.Azure.Cosmos/tests/Microsoft.Azure.Cosmos.Tests/ChangeFeed/DocumentServiceLeaseManagerCosmosTests.cs
+++ b/Microsoft.Azure.Cosmos/tests/Microsoft.Azure.Cosmos.Tests/ChangeFeed/DocumentServiceLeaseManagerCosmosTests.cs
@@ -628,6 +628,13 @@ private static void ValidateRequestOptionsFactory(RequestOptionsFactory requestO
             else if (requestOptionsFactory is PartitionedByPartitionKeyCollectionRequestOptionsFactory)
             {
                 Assert.IsNotNull(lease.PartitionKey);
+
+                // The lease's partition-key value must equal its id so that concurrent/retry creates
+                // for the same lease resolve to the same (id, partitionKey) tuple and Cosmos's per-
+                // partition-key id-uniqueness check turns duplicates into a 409 Conflict. Using a
+                // random Guid here would silently persist cross-partition-key duplicates and stall
+                // the change feed load balancer. See DocumentServiceLeaseManagerCosmos.CreateLeaseIfNotExistAsync.
+                Assert.AreEqual(lease.Id, lease.PartitionKey);
             }
             else
             {