diff --git a/SDL3-CS/Properties/AssemblyInfo.cs b/SDL3-CS/Properties/AssemblyInfo.cs
new file mode 100644
index 0000000..4fabb01
--- /dev/null
+++ b/SDL3-CS/Properties/AssemblyInfo.cs
@@ -0,0 +1,6 @@
+// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
+// See the LICENCE file in the repository root for full licence text.
+
+using System.Runtime.CompilerServices;
+
+[assembly: InternalsVisibleTo("SDL3-CS.Tests")]
diff --git a/SDL3-CS/Utf8String.cs b/SDL3-CS/Utf8String.cs
index 253ee87..d50fc8c 100644
--- a/SDL3-CS/Utf8String.cs
+++ b/SDL3-CS/Utf8String.cs
@@ -13,7 +13,7 @@ namespace SDL
     /// <remarks>Should only be instantiated through implicit conversions.</remarks>
     public readonly ref struct Utf8String
     {
-        public readonly ReadOnlySpan<byte> Raw;
+        internal readonly ReadOnlySpan<byte> Raw;
 
         private Utf8String(ReadOnlySpan<byte> raw)
         {