diff --git a/src/CrockfordBase32/CrockfordBase32.csproj b/src/CrockfordBase32/CrockfordBase32.csproj
index 4dd27e7..fbe882a 100644
--- a/src/CrockfordBase32/CrockfordBase32.csproj
+++ b/src/CrockfordBase32/CrockfordBase32.csproj
@@ -3,7 +3,7 @@
   <PropertyGroup>
     <TargetFrameworks>netstandard2.0;netstandard2.1</TargetFrameworks>
     <Title>CrockfordBase32</Title>
-	<Version>2.0.0-alpha2</Version>
+	<Version>2.0.0-alpha3</Version>
 	<Authors>Tatham Oddie, jonsagara</Authors>
 	<Description>A .NET Standard implementation of Crockford's Base32 encoding that works great for URLs and humans.</Description>
     <Company>Tatham Oddie</Company>
@@ -27,6 +27,10 @@
 
     <!-- Optional: Include the PDB in the built .nupkg -->
     <AllowedOutputExtensionsInPackageBuildOutputFolder>$(AllowedOutputExtensionsInPackageBuildOutputFolder);.pdb</AllowedOutputExtensionsInPackageBuildOutputFolder>
+
+	<!-- Use nullable reference types -->
+	<LangVersion>8.0</LangVersion>
+	<Nullable>enable</Nullable>
   </PropertyGroup>
   <ItemGroup>
     <PackageReference Include="Microsoft.SourceLink.GitHub" Version="1.0.0" PrivateAssets="All" />
diff --git a/src/CrockfordBase32/SymbolDefinition.cs b/src/CrockfordBase32/SymbolDefinition.cs
index 8ad3c5b..c521ae7 100644
--- a/src/CrockfordBase32/SymbolDefinition.cs
+++ b/src/CrockfordBase32/SymbolDefinition.cs
@@ -5,7 +5,7 @@ namespace CrockfordBase32
     internal class SymbolDefinition
     {
         public int Value { get; set; }
-        public IEnumerable<char> DecodeSymbols { get; set; }
+        public IEnumerable<char> DecodeSymbols { get; set; } = null!;
         public char EncodeSymbol { get; set; }
     }
 }
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