diff --git a/Rnwood.Smtp4dev/Rnwood.Smtp4dev.csproj b/Rnwood.Smtp4dev/Rnwood.Smtp4dev.csproj
index 1e42af762..d3bbbe782 100644
--- a/Rnwood.Smtp4dev/Rnwood.Smtp4dev.csproj
+++ b/Rnwood.Smtp4dev/Rnwood.Smtp4dev.csproj
@@ -20,7 +20,7 @@
 	</PropertyGroup>
 
 	<ItemGroup>
-		<PackageReference Include="Ardalis.GuardClauses" Version="3.3.0" />
+		<PackageReference Include="Ardalis.GuardClauses" Version="4.0.0" />
 		<PackageReference Include="CommandLiners.MonoOptions" Version="1.0.36" />
 		<PackageReference Include="HtmlAgilityPack" Version="1.11.40" />
 		<PackageReference Include="MailKit" Version="2.15.0" />