diff --git a/src/ZB.MOM.WW.ScadaBridge.TemplateEngine/Flattening/DiffService.cs b/src/ZB.MOM.WW.ScadaBridge.TemplateEngine/Flattening/DiffService.cs
index e32d1bbc..532e63ef 100644
--- a/src/ZB.MOM.WW.ScadaBridge.TemplateEngine/Flattening/DiffService.cs
+++ b/src/ZB.MOM.WW.ScadaBridge.TemplateEngine/Flattening/DiffService.cs
@@ -142,6 +142,7 @@ public class DiffService
         a.Description == b.Description &&
         a.PriorityLevel == b.PriorityLevel &&
         a.IsLocked == b.IsLocked &&
+        a.IsMesReportable == b.IsMesReportable &&
         a.TriggerType == b.TriggerType &&
         a.TriggerConfiguration == b.TriggerConfiguration &&
         a.OnTriggerScriptCanonicalName == b.OnTriggerScriptCanonicalName;
diff --git a/src/ZB.MOM.WW.ScadaBridge.TemplateEngine/Flattening/RevisionHashService.cs b/src/ZB.MOM.WW.ScadaBridge.TemplateEngine/Flattening/RevisionHashService.cs
index 9c8ad5f1..f240e3be 100644
--- a/src/ZB.MOM.WW.ScadaBridge.TemplateEngine/Flattening/RevisionHashService.cs
+++ b/src/ZB.MOM.WW.ScadaBridge.TemplateEngine/Flattening/RevisionHashService.cs
@@ -78,6 +78,8 @@ public class RevisionHashService
                     Description = a.Description,
                     PriorityLevel = a.PriorityLevel,
                     IsLocked = a.IsLocked,
+                    // true-only (null when false) so existing revision hashes are unchanged.
+                    IsMesReportable = a.IsMesReportable ? true : null,
                     TriggerType = a.TriggerType,
                     TriggerConfiguration = a.TriggerConfiguration,
                     OnTriggerScriptCanonicalName = a.OnTriggerScriptCanonicalName
@@ -242,6 +244,11 @@ public class RevisionHashService
         /// </summary>
         public bool IsLocked { get; init; }
         /// <summary>
+        /// MES-reportable flag; null when false (the serializer drops nulls), so
+        /// pre-existing configurations hash identically.
+        /// </summary>
+        public bool? IsMesReportable { get; init; }
+        /// <summary>
         /// The canonical name of the script triggered by this alarm.
         /// </summary>
         public string? OnTriggerScriptCanonicalName { get; init; }
diff --git a/tests/ZB.MOM.WW.ScadaBridge.TemplateEngine.Tests/Flattening/DiffServiceTests.cs b/tests/ZB.MOM.WW.ScadaBridge.TemplateEngine.Tests/Flattening/DiffServiceTests.cs
index 9c9b516f..83cdf7b4 100644
--- a/tests/ZB.MOM.WW.ScadaBridge.TemplateEngine.Tests/Flattening/DiffServiceTests.cs
+++ b/tests/ZB.MOM.WW.ScadaBridge.TemplateEngine.Tests/Flattening/DiffServiceTests.cs
@@ -230,6 +230,28 @@ public class DiffServiceTests
         Assert.Equal(DiffChangeType.Changed, diff.AlarmChanges[0].ChangeType);
     }
 
+    /// <summary>Gitea #102: flipping a computed alarm's MES-reportable flag is a diff.</summary>
+    [Fact]
+    public void ComputeDiff_AlarmIsMesReportableChange_DetectedAsChanged()
+    {
+        var oldConfig = new FlattenedConfiguration
+        {
+            InstanceUniqueName = "Instance1",
+            Alarms = [new ResolvedAlarm { CanonicalName = "HighTemp", TriggerType = "RangeViolation" }]
+        };
+        var newConfig = new FlattenedConfiguration
+        {
+            InstanceUniqueName = "Instance1",
+            Alarms = [new ResolvedAlarm { CanonicalName = "HighTemp", TriggerType = "RangeViolation", IsMesReportable = true }]
+        };
+
+        var diff = _sut.ComputeDiff(oldConfig, newConfig);
+
+        Assert.True(diff.HasChanges);
+        Assert.Single(diff.AlarmChanges);
+        Assert.Equal(DiffChangeType.Changed, diff.AlarmChanges[0].ChangeType);
+    }
+
     /// <summary>Verifies that a native alarm source reference change is detected as changed.</summary>
     [Fact]
     public void ComputeDiff_NativeAlarmSourceReferenceChange_DetectedAsChanged()
diff --git a/tests/ZB.MOM.WW.ScadaBridge.TemplateEngine.Tests/Flattening/RevisionHashServiceTests.cs b/tests/ZB.MOM.WW.ScadaBridge.TemplateEngine.Tests/Flattening/RevisionHashServiceTests.cs
index 5d535be5..e2d13948 100644
--- a/tests/ZB.MOM.WW.ScadaBridge.TemplateEngine.Tests/Flattening/RevisionHashServiceTests.cs
+++ b/tests/ZB.MOM.WW.ScadaBridge.TemplateEngine.Tests/Flattening/RevisionHashServiceTests.cs
@@ -191,6 +191,24 @@ public class RevisionHashServiceTests
         Assert.NotEqual(_sut.ComputeHash(configBefore), _sut.ComputeHash(configAfter));
     }
 
+    /// <summary>Gitea #102: the computed alarm's MES-reportable flag participates in the hash; false hashes as before the field existed.</summary>
+    [Fact]
+    public void ComputeHash_AlarmIsMesReportableChange_ChangesHash()
+    {
+        var baseAlarm = new ResolvedAlarm { CanonicalName = "HighTemp", TriggerType = "RangeViolation" };
+        var configFalse = new FlattenedConfiguration
+        {
+            InstanceUniqueName = "Instance1", TemplateId = 1, SiteId = 1,
+            Alarms = [baseAlarm]
+        };
+        var configTrue = configFalse with { Alarms = [baseAlarm with { IsMesReportable = true }] };
+
+        Assert.NotEqual(_sut.ComputeHash(configFalse), _sut.ComputeHash(configTrue));
+        // false is omitted from the canonical JSON, so adding the field cannot invalidate stored hashes.
+        Assert.Equal(_sut.ComputeHash(configFalse),
+            _sut.ComputeHash(configFalse with { Alarms = [baseAlarm with { IsMesReportable = false }] }));
+    }
+
     /// <summary>Verifies that editing a connection endpoint changes the hash.</summary>
     [Fact]
     public void ComputeHash_ConnectionEndpointEdit_ChangesHash()