diff --git a/tests/Avalonia.UnitTests/MockPlatformRenderInterface.cs b/tests/Avalonia.UnitTests/MockPlatformRenderInterface.cs
index b65c40cedd..0e2abb314d 100644
--- a/tests/Avalonia.UnitTests/MockPlatformRenderInterface.cs
+++ b/tests/Avalonia.UnitTests/MockPlatformRenderInterface.cs
@@ -9,7 +9,7 @@ namespace Avalonia.UnitTests
 {
     public class MockPlatformRenderInterface : IPlatformRenderInterface
     {
-        public IEnumerable<string> InstalledFontNames => Mock.Of<IEnumerable<string>>();
+        public IEnumerable<string> InstalledFontNames => new string[0];
 
         public IFormattedTextImpl CreateFormattedText(
             string text,
diff --git a/tests/Avalonia.Visuals.UnitTests/VisualTree/MockRenderInterface.cs b/tests/Avalonia.Visuals.UnitTests/VisualTree/MockRenderInterface.cs
index bd46e68fd8..fec0f0831a 100644
--- a/tests/Avalonia.Visuals.UnitTests/VisualTree/MockRenderInterface.cs
+++ b/tests/Avalonia.Visuals.UnitTests/VisualTree/MockRenderInterface.cs
@@ -8,7 +8,7 @@ namespace Avalonia.Visuals.UnitTests.VisualTree
 {
     class MockRenderInterface : IPlatformRenderInterface
     {
-        public IEnumerable<string> InstalledFontNames => throw new NotImplementedException();
+        public IEnumerable<string> InstalledFontNames => new string[0];
 
         public IFormattedTextImpl CreateFormattedText(
             string text,