diff --git a/src/Hl7.Fhir.Base/FhirPath/ElementNavFhirExtensions.cs b/src/Hl7.Fhir.Base/FhirPath/ElementNavFhirExtensions.cs
index e66eb4fe7b..468bfb6f6b 100644
--- a/src/Hl7.Fhir.Base/FhirPath/ElementNavFhirExtensions.cs
+++ b/src/Hl7.Fhir.Base/FhirPath/ElementNavFhirExtensions.cs
@@ -283,7 +283,7 @@ internal static P.Time BoundaryTime(P.Time time, long? precision, int minutes, i
                 "code" when input is ScopedNode sn => inParams.WithCode(code: sn.Value as string, context: sn.LocalLocation),
                 "Coding" => inParams.WithCoding(input.ParseCoding()),
                 "CodeableConcept" => inParams.WithCodeableConcept(input.ParseCodeableConcept()),
-                "System.String" => inParams.WithCode(code: input.Value as string, context: "No context available"),
+                "string" or "System.String" => inParams.WithCode(code: input.Value as string, context: "No context available"),
                 _ => null,
             };
 
diff --git a/src/Hl7.FhirPath.R4.Tests/PocoTests/FhirPathTest.cs b/src/Hl7.FhirPath.R4.Tests/PocoTests/FhirPathTest.cs
index d9b9f5c926..fb2810ce09 100644
--- a/src/Hl7.FhirPath.R4.Tests/PocoTests/FhirPathTest.cs
+++ b/src/Hl7.FhirPath.R4.Tests/PocoTests/FhirPathTest.cs
@@ -383,6 +383,12 @@ public static IEnumerable<object[]> MemberOfTestData()
                                             }, "memberOf('http://hl7.org/fhir/ValueSet/observation-vitalsignresult')", true };
 
             // memberOf with string objects
+            yield return new object[] { new FhirString("85353-1"), "memberOf('http://hl7.org/fhir/ValueSet/observation-vitalsignresult')", true };
+            yield return new object[] { new FhirString("male"), "memberOf('http://hl7.org/fhir/ValueSet/administrative-gender')", true };
+            yield return new object[] { new FhirString("female"), "memberOf('http://hl7.org/fhir/ValueSet/administrative-gender')", true };
+            yield return new object[] { new FhirString("no-idea"), "memberOf('http://hl7.org/fhir/ValueSet/administrative-gender')", false };
+
+            // memberOf with inline string objects
             yield return new object[] { new FhirBoolean(), "'85353-1'.memberOf('http://hl7.org/fhir/ValueSet/observation-vitalsignresult')", true };
             yield return new object[] { new FhirBoolean(), "'male'.memberOf('http://hl7.org/fhir/ValueSet/administrative-gender')", true };
             yield return new object[] { new FhirBoolean(), "'female'.memberOf('http://hl7.org/fhir/ValueSet/administrative-gender')", true };