diff --git a/Charts/TitlesIni.cs b/Charts/TitlesIni.cs
index 3ce159d..a783958 100644
--- a/Charts/TitlesIni.cs
+++ b/Charts/TitlesIni.cs
@@ -16,6 +16,10 @@ namespace SabreTools.Models.Charts
         /// `name` - Display name of the tier.
         /// `unlock_id` - Name used for associating a song with this tier, and for checking unlock requirements.
         /// </summary>
+#if NET20 || NET35
+        public Dictionary<string, System.Tuple<string?, string?>>? Sections { get; set; }
+#else
         public Dictionary<string, (string? Name, string? UnlockId)>? Sections { get; set; }
+#endif
     }
 }
\ No newline at end of file
diff --git a/Metadata/DictionaryBase.cs b/Metadata/DictionaryBase.cs
index cbd5c9f..364a55d 100644
--- a/Metadata/DictionaryBase.cs
+++ b/Metadata/DictionaryBase.cs
@@ -100,7 +100,7 @@ namespace SabreTools.Models.Metadata
 
             string[]? asArray = Read<string[]>(key);
             if (asArray != null)
-#if NET48
+#if NETFRAMEWORK
                 return string.Join(",", asArray);
 #else
                 return string.Join(',', asArray);
@@ -140,7 +140,11 @@ namespace SabreTools.Models.Metadata
         /// </summary>
         private bool ValidateKey(string key)
         {
+#if NET20 || NET35
+            if (key == null || string.IsNullOrEmpty(key.TrimEnd(' ')))
+#else
             if (string.IsNullOrWhiteSpace(key))
+#endif
                 return false;
             else if (!ContainsKey(key))
                 return false;
diff --git a/SabreTools.Models.csproj b/SabreTools.Models.csproj
index 1ca0aaf..3dd82cd 100644
--- a/SabreTools.Models.csproj
+++ b/SabreTools.Models.csproj
@@ -2,7 +2,7 @@
 
   <PropertyGroup>
     <!-- Assembly Properties -->
-    <TargetFrameworks>net48;netcoreapp3.1;net6.0;net7.0;net8.0</TargetFrameworks>
+    <TargetFrameworks>net20;net35;net40;net452;net462;net472;net48;netcoreapp3.1;net6.0;net7.0;net8.0</TargetFrameworks>
     <RuntimeIdentifiers>win-x86;win-x64;win-arm64;linux-x64;linux-arm64;osx-x64;osx-arm64</RuntimeIdentifiers>
     <LangVersion>latest</LangVersion>
     <Nullable>enable</Nullable>
@@ -24,6 +24,17 @@
     <None Include="README.md" Pack="true" PackagePath=""/>
   </ItemGroup>
 
+  <!-- Support for old .NET versions -->
+  <ItemGroup Condition="$(TargetFramework.StartsWith(`net4`))">
+    <PackageReference Include="System.ValueTuple" Version="4.5.0" />
+  </ItemGroup>
+  <ItemGroup Condition="$(TargetFramework.StartsWith(`net3`))">
+    <PackageReference Include="NetLegacySupport.Tuple" Version="1.1.1" />
+  </ItemGroup>
+  <ItemGroup Condition="$(TargetFramework.StartsWith(`net2`))">
+    <PackageReference Include="NetLegacySupport.Tuple" Version="1.1.1" />
+  </ItemGroup>
+
   <ItemGroup>
     <PackageReference Include="Newtonsoft.Json" Version="13.0.3" />
   </ItemGroup>