diff --git a/test/Discord.Net.Tests.Unit/Discord.Net.Tests.Unit.csproj b/test/Discord.Net.Tests.Unit/Discord.Net.Tests.Unit.csproj
index 087a64d834..937a5fb948 100644
--- a/test/Discord.Net.Tests.Unit/Discord.Net.Tests.Unit.csproj
+++ b/test/Discord.Net.Tests.Unit/Discord.Net.Tests.Unit.csproj
@@ -14,7 +14,7 @@
   <ItemGroup>
     <PackageReference Include="FluentAssertions" Version="6.7.0" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="16.11.0" />
-    <PackageReference Include="Moq" Version="4.18.1" />
+    <PackageReference Include="NSubstitute" Version="5.0.0" />
     <PackageReference Include="xunit" Version="2.4.1" />
     <PackageReference Include="xunit.runner.visualstudio" Version="2.4.3">
       <PrivateAssets>all</PrivateAssets>
diff --git a/test/Discord.Net.Tests.Unit/GuildHelperTests.cs b/test/Discord.Net.Tests.Unit/GuildHelperTests.cs
index aa4ee329c1..c6c544c96d 100644
--- a/test/Discord.Net.Tests.Unit/GuildHelperTests.cs
+++ b/test/Discord.Net.Tests.Unit/GuildHelperTests.cs
@@ -1,6 +1,5 @@
 using Discord.Rest;
-using FluentAssertions;
-using Moq;
+using NSubstitute;
 using System;
 using Xunit;
 
@@ -15,11 +14,13 @@ public class GuildHelperTests
     [InlineData(PremiumTier.Tier3, 100)]
     public void GetUploadLimit(PremiumTier tier, ulong factor)
     {
-        var guild = Mock.Of<IGuild>(g => g.PremiumTier == tier);
+        var guild = Substitute.For<IGuild>();
+        guild.PremiumTier.Returns(tier);
+
         var expected = factor * (ulong)Math.Pow(2, 20);
 
         var actual = GuildHelper.GetUploadLimit(guild);
 
-        actual.Should().Be(expected);
+        Assert.Equal(expected, actual);
     }
 }