diff --git a/src/Nitride.Temporal/CreateDateIndexes.cs b/src/Nitride.Temporal/CreateDateIndexes.cs
index e6cf27b..ceb9b30 100644
--- a/src/Nitride.Temporal/CreateDateIndexes.cs
+++ b/src/Nitride.Temporal/CreateDateIndexes.cs
@@ -113,7 +113,7 @@ public partial class CreateDateIndexes : OperationBase, IResolvingOperation
                     : new List<Entity>();
 
                 // Create the index then add it to the output list.
-                var index = new DateIndex(pair.Key, childEntities, childIndexes);
+                var index = new DateIndex(pair.Key, this.Formats[i], childEntities, childIndexes);
                 Entity? indexEntity = this.CreateIndex!(index);
 
                 output.Add(indexEntity);
diff --git a/src/Nitride.Temporal/DateIndex.cs b/src/Nitride.Temporal/DateIndex.cs
index 47c462c..66619d7 100644
--- a/src/Nitride.Temporal/DateIndex.cs
+++ b/src/Nitride.Temporal/DateIndex.cs
@@ -6,9 +6,10 @@ namespace Nitride.Temporal;
 
 public class DateIndex
 {
-    public DateIndex(string key, IReadOnlyList<Entity> entries, IReadOnlyList<Entity> indexes)
+    public DateIndex(string key, string format, IReadOnlyList<Entity> entries, IReadOnlyList<Entity> indexes)
     {
         this.Key = key;
+        this.Format = format;
         this.Entries = entries;
         this.Indexes = indexes;
     }
@@ -18,6 +19,11 @@ public class DateIndex
     /// </summary>
     public IReadOnlyList<Entity> Entries { get; }
 
+    /// <summary>
+    /// Gets the format used to create this index.
+    /// </summary>
+    public string Format { get; }
+
     /// <summary>
     /// Gets the ordered list of nested indexes, if there are any. This will be an
     /// empty list if the index has no
diff --git a/tests/Nitride.Temporal.Tests/CreateDateIndexesTests.cs b/tests/Nitride.Temporal.Tests/CreateDateIndexesTests.cs
index 84e1811..1e11deb 100644
--- a/tests/Nitride.Temporal.Tests/CreateDateIndexesTests.cs
+++ b/tests/Nitride.Temporal.Tests/CreateDateIndexesTests.cs
@@ -84,7 +84,7 @@ public class CreateDateIndexesTests : TemporalTestBase
 
         TestHelper.CompareObjects(expected, actual);
     }
-    
+
     [Fact]
     public void YearMonthDayIndexesThreshold1()
     {