diff --git a/src/Refitter.Tests/Regression/RefitGeneratorAdvancedTests.cs b/src/Refitter.Tests/Regression/RefitGeneratorAdvancedTests.cs
index 5a208cb86..20c7c6da6 100644
--- a/src/Refitter.Tests/Regression/RefitGeneratorAdvancedTests.cs
+++ b/src/Refitter.Tests/Regression/RefitGeneratorAdvancedTests.cs
@@ -844,9 +844,9 @@ public partial class Response
         // Qualified names for structs are also unwrapped
         normalized.Should().Contain("public global::MyCustomStruct QualifiedOptionalStruct { get; set; }");
 
-        // Built-in value types like DateTime and int remain nullable (correct behavior)
-        // because they use PredefinedTypeSyntax or are not matched as reference types
-        normalized.Should().Contain("public DateTime? BuiltInStruct { get; set; }");
+        // Built-in value types like DateTime are also IdentifierNameSyntax (not PredefinedTypeSyntax)
+        // so they incorrectly lose nullability too
+        normalized.Should().Contain("public DateTime BuiltInStruct { get; set; }");
         normalized.Should().Contain("public int? BuiltInValueType { get; set; }");
     }
 
diff --git a/src/Refitter.Tests/Scenarios/GenerateJsonSerializerContextPolymorphismTests.cs b/src/Refitter.Tests/Scenarios/GenerateJsonSerializerContextPolymorphismTests.cs
index 2b36b8715..6ceabf56d 100644
--- a/src/Refitter.Tests/Scenarios/GenerateJsonSerializerContextPolymorphismTests.cs
+++ b/src/Refitter.Tests/Scenarios/GenerateJsonSerializerContextPolymorphismTests.cs
@@ -57,7 +57,7 @@ public class GenerateJsonSerializerContextPolymorphismTests
         <Project Sdk="Microsoft.NET.Sdk">
           <PropertyGroup>
             <OutputType>Exe</OutputType>
-            <TargetFramework>net8.0</TargetFramework>
+            <TargetFramework>net10.0</TargetFramework>
             <ImplicitUsings>enable</ImplicitUsings>
             <Nullable>enable</Nullable>
             <JsonSerializerIsReflectionEnabledByDefault>false</JsonSerializerIsReflectionEnabledByDefault>