diff --git a/src/libraries/System.Net.Http.Json/tests/FunctionalTests/System.Net.Http.Json.Functional.Tests.csproj b/src/libraries/System.Net.Http.Json/tests/FunctionalTests/System.Net.Http.Json.Functional.Tests.csproj
index fdc00db7ae3f17..b16cea2304f960 100644
--- a/src/libraries/System.Net.Http.Json/tests/FunctionalTests/System.Net.Http.Json.Functional.Tests.csproj
+++ b/src/libraries/System.Net.Http.Json/tests/FunctionalTests/System.Net.Http.Json.Functional.Tests.csproj
@@ -2,6 +2,7 @@
 
   <PropertyGroup>
     <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkCurrent)</TargetFrameworks>
+    <JsonSerializerIsReflectionEnabledByDefault>true</JsonSerializerIsReflectionEnabledByDefault>
   </PropertyGroup>
 
   <ItemGroup>
diff --git a/src/libraries/System.Net.Http.Json/tests/UnitTests/System.Net.Http.Json.Unit.Tests.csproj b/src/libraries/System.Net.Http.Json/tests/UnitTests/System.Net.Http.Json.Unit.Tests.csproj
index 447b136bf972de..ddfaa0f52cecbf 100644
--- a/src/libraries/System.Net.Http.Json/tests/UnitTests/System.Net.Http.Json.Unit.Tests.csproj
+++ b/src/libraries/System.Net.Http.Json/tests/UnitTests/System.Net.Http.Json.Unit.Tests.csproj
@@ -1,6 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkMinimum)</TargetFrameworks>
+    <JsonSerializerIsReflectionEnabledByDefault>true</JsonSerializerIsReflectionEnabledByDefault>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="TranscodingReadStreamTests.cs" />