diff --git a/src/Microsoft.Health.Fhir.SpecManager/Language/CSharpFirely2.cs b/src/Microsoft.Health.Fhir.SpecManager/Language/CSharpFirely2.cs
index 3dd0fa01a..dff6cefbe 100644
--- a/src/Microsoft.Health.Fhir.SpecManager/Language/CSharpFirely2.cs
+++ b/src/Microsoft.Health.Fhir.SpecManager/Language/CSharpFirely2.cs
@@ -1492,11 +1492,24 @@ private void WriteCodedElement(
                 element,
                 subset,
                 out string summary,
+                out string isModifier,
                 out string choice,
                 out string allowedTypes,
                 out string resourceReferences);
 
-            _writer.WriteLineIndented($"[FhirElement(\"{element.Name}\"{summary}, Order={GetOrder(element)}{choice})]");
+            /* Exceptions:
+            *  o OperationOutcome.issue.severity does not have `IsModifier` anymore since R4. 
+            */
+
+            if (element.Path == "OperationOutcome.issue.severity")
+            {
+                _writer.WriteLineIndented($"[FhirElement(\"{element.Name}\"{summary}, IsModifier=true, Order={GetOrder(element)}{choice})]");
+                _writer.WriteLineIndented($"[FhirElement(\"{element.Name}\"{summary}, Order={GetOrder(element)}{choice}, Since=FhirRelease.R4)]");
+            }
+            else
+            {
+                _writer.WriteLineIndented($"[FhirElement(\"{element.Name}\"{summary}{isModifier}, Order={GetOrder(element)}{choice})]");
+            }
 
             if (hasDefinedEnum)
             {
@@ -1686,6 +1699,7 @@ private void WriteElement(
                 element,
                 subset,
                 out string summary,
+                out string isModifier,
                 out string choice,
                 out string allowedTypes,
                 out string resourceReferences);
@@ -1698,15 +1712,15 @@ private void WriteElement(
              * automate this, by scanning differences between 3/4/5/6/7 etc.. */
             if (element.Path == "Meta.source")
             {
-                _writer.WriteLineIndented($"[FhirElement(\"{name}\"{summary}, Order={GetOrder(element)}{choice}, Since=FhirRelease.R4)]");
+                _writer.WriteLineIndented($"[FhirElement(\"{name}\"{summary}{isModifier}, Order={GetOrder(element)}{choice}, Since=FhirRelease.R4)]");
             }
             else if (element.Path == "Reference.type")
             {
-                _writer.WriteLineIndented($"[FhirElement(\"{name}\"{summary}, Order={GetOrder(element)}{choice}, Since=FhirRelease.R4)]");
+                _writer.WriteLineIndented($"[FhirElement(\"{name}\"{summary}{isModifier}, Order={GetOrder(element)}{choice}, Since=FhirRelease.R4)]");
             }
             else
             {
-                _writer.WriteLineIndented($"[FhirElement(\"{name}\"{summary}, Order={GetOrder(element)}{choice})]");
+                _writer.WriteLineIndented($"[FhirElement(\"{name}\"{summary}{isModifier}, Order={GetOrder(element)}{choice})]");
             }
 
             if (element.Path == "Meta.profile")
@@ -1991,6 +2005,7 @@ private void BuildElementOptionals(
             FhirElement element,
             GenSubset subset,
             out string summary,
+            out string isModifier,
             out string choice,
             out string allowedTypes,
             out string resourceReferences)
@@ -1999,6 +2014,7 @@ private void BuildElementOptionals(
             allowedTypes = string.Empty;
             resourceReferences = string.Empty;
             summary = element.IsSummary ? ", InSummary=true" : string.Empty;
+            isModifier = element.IsModifier ? ", IsModifier=true" : string.Empty;
 
             bool inCommon = subset.HasFlag(GenSubset.Common);
 
diff --git a/src/Microsoft.Health.Fhir.SpecManager/Models/FhirElement.cs b/src/Microsoft.Health.Fhir.SpecManager/Models/FhirElement.cs
index aa91ce5d5..dc4b4c23b 100644
--- a/src/Microsoft.Health.Fhir.SpecManager/Models/FhirElement.cs
+++ b/src/Microsoft.Health.Fhir.SpecManager/Models/FhirElement.cs
@@ -8,7 +8,6 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
-using System.Text;
 using Microsoft.Health.Fhir.SpecManager.Extensions;
 
 namespace Microsoft.Health.Fhir.SpecManager.Models
@@ -141,7 +140,7 @@ public FhirElement(
             }
 
             IsModifier = isModifier == true;
-            IsSummary = (isSummary == true) || IsModifier;
+            IsSummary = isSummary == true;
 
             DefaultFieldName = defaultFieldName;
             DefaultFieldValue = defaultFieldValue;