diff --git a/X10D.Tests/src/Drawing/PointFTests.cs b/X10D.Tests/src/Drawing/PointFTests.cs
index 52c33bc..87b6f63 100644
--- a/X10D.Tests/src/Drawing/PointFTests.cs
+++ b/X10D.Tests/src/Drawing/PointFTests.cs
@@ -1,5 +1,8 @@
 using System.Drawing;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
+#if !NET6_0_OR_GREATER
+using X10D.Core;
+#endif
 using X10D.Drawing;
 
 namespace X10D.Tests.Drawing;
diff --git a/X10D.Tests/src/Math/MathUtilityTests.cs b/X10D.Tests/src/Math/MathUtilityTests.cs
index 3e4bf52..d8b8c7d 100644
--- a/X10D.Tests/src/Math/MathUtilityTests.cs
+++ b/X10D.Tests/src/Math/MathUtilityTests.cs
@@ -1,4 +1,7 @@
 using Microsoft.VisualStudio.TestTools.UnitTesting;
+#if !NET6_0_OR_GREATER
+using X10D.Core;
+#endif
 using X10D.Math;
 
 namespace X10D.Tests.Math;
diff --git a/X10D.Tests/src/Numerics/Vector2Tests.cs b/X10D.Tests/src/Numerics/Vector2Tests.cs
index 25389b7..a0497e8 100644
--- a/X10D.Tests/src/Numerics/Vector2Tests.cs
+++ b/X10D.Tests/src/Numerics/Vector2Tests.cs
@@ -1,5 +1,8 @@
 using System.Numerics;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
+#if !NET6_0_OR_GREATER
+using X10D.Core;
+#endif
 using X10D.Drawing;
 using X10D.Numerics;