diff --git a/README.ja.md b/README.ja.md
index b76e74e..c46076b 100644
--- a/README.ja.md
+++ b/README.ja.md
@@ -460,6 +460,8 @@ nuspecファイルを使ってパッケージを生成する場合は、デフ
 
 ## 履歴
 
+* 3.2.60:
+  * ビルド時に`ThisAssembly`シンボルが参照できない場合があるのを修正。
 * 3.2.50:
   * 同じコミットに複数のバージョンタグが含まれる場合に、最も大きいバージョン番号を使用するように改良。
 * 3.2.40:
diff --git a/README.md b/README.md
index 4f90e87..2ce3433 100644
--- a/README.md
+++ b/README.md
@@ -439,6 +439,8 @@ When you are using a nuspec file to generate a NuGet package, there are addition
 
 ## History
 
+* 3.2.60:
+  * Fixed the `ThisAssembly` symbol could not be referenced at build time.
 * 3.2.50:
   * Improved to use the highest version number when multiple version tags are included in the same commit.
 * 3.2.40:
diff --git a/RelaxVersioner.Core/Analyzer.cs b/RelaxVersioner.Core/Analyzer.cs
index ae59407..214d33e 100644
--- a/RelaxVersioner.Core/Analyzer.cs
+++ b/RelaxVersioner.Core/Analyzer.cs
@@ -92,7 +92,8 @@ private static async Task<Version> LookupVersionLabelAsync(
 
             // Detected mostly larger version tag.
             var candidates = commit.Tags.
-                Collect(tag => Version.TryParse(tag.Name, out var v) ? v : null!).
+                Select(tag => Version.TryParse(tag.Name, out var v) ? v : null!).
+                Where(v => v != null).
                 OrderByDescending(v => v).
                 ToArray();
             if (candidates.Length >= 1)
@@ -102,7 +103,6 @@ private static async Task<Version> LookupVersionLabelAsync(
                 break;
             }
 
-            // Traverse next commits.
             var parents = await commit.GetParentCommitsAsync(ct);
             if (parents.Length == 0)
             {
diff --git a/RelaxVersioner.Core/RelaxVersioner.Core.csproj b/RelaxVersioner.Core/RelaxVersioner.Core.csproj
index 6721130..0076318 100644
--- a/RelaxVersioner.Core/RelaxVersioner.Core.csproj
+++ b/RelaxVersioner.Core/RelaxVersioner.Core.csproj
@@ -16,7 +16,7 @@
     <PackageReference Include="NamingFormatter" Version="2.3.0" />
     <PackageReference Include="Microsoft.NETFramework.ReferenceAssemblies" Version="1.0.3" PrivateAssets="All" />
     <PackageReference Condition="'$(RV_BOOTSTRAP)' != 'True'"
-                      Include="RelaxVersioner" Version="*" PrivateAssets="all" />
+                      Include="RelaxVersioner" Version="3.2.40" PrivateAssets="all" />
   </ItemGroup>
 
   <ItemGroup>
diff --git a/RelaxVersioner.Core/Utilities.cs b/RelaxVersioner.Core/Utilities.cs
index 57776fa..53d2a72 100644
--- a/RelaxVersioner.Core/Utilities.cs
+++ b/RelaxVersioner.Core/Utilities.cs
@@ -7,8 +7,6 @@
 //
 ////////////////////////////////////////////////////////////////////////////////////////
 
-#nullable enable
-
 using System;
 using System.Collections.Generic;
 using System.Diagnostics;
@@ -43,12 +41,12 @@ public static Dictionary<string, WriterBase> GetWriters()
         return typeof(Utilities).Assembly.
             GetTypes().
             Where(type => type.IsSealed && type.IsClass && typeof(WriterBase).IsAssignableFrom(type)).
-            Select(type => (WriterBase)Activator.CreateInstance(type)!).
+            Select(type => (WriterBase)Activator.CreateInstance(type)).
             ToDictionary(writer => writer.Language, StringComparer.InvariantCultureIgnoreCase);
     }
 
-    private static async Task<T?> TraversePathToRootAsync<T>(
-        string candidatePath, Func<string, Task<T?>> action)
+    private static async Task<T> TraversePathToRootAsync<T>(
+        string candidatePath, Func<string, Task<T>> action)
         where T : class
     {
         var path = Path.GetFullPath(candidatePath).
@@ -78,7 +76,7 @@ public static string GetDirectoryNameWithoutTrailingSeparator(string path) =>
     public static string GetDirectoryNameWithTrailingSeparator(string path) =>
         GetDirectoryNameWithoutTrailingSeparator(path) + Path.DirectorySeparatorChar;
 
-    public static async Task<StructuredRepository?> OpenRepositoryAsync(
+    public static async Task<StructuredRepository> OpenRepositoryAsync(
         Logger logger, string candidatePath)
     {
         var repository = await TraversePathToRootAsync(candidatePath, async path =>
@@ -105,30 +103,15 @@ public static string GetDirectoryNameWithTrailingSeparator(string path) =>
         return repository;
     }
 
-    public static IEnumerable<U> Collect<T, U>(
-        this IEnumerable<T> enumerable,
-        Func<T, U?> selector)
-        where U : class
-    {
-        foreach (var item in enumerable)
-        {
-            if (selector(item) is { } value)
-            {
-                yield return value;
-            }
-        }
-    }
-
     public static TValue GetValue<TKey, TValue>(
         this Dictionary<TKey, TValue> dictionary,
         TKey key,
         TValue defaultValue)
-        where TKey : notnull
     {
         Debug.Assert(dictionary != null);
         Debug.Assert(key != null);
 
-        if (dictionary!.TryGetValue(key!, out var value) == false)
+        if (dictionary.TryGetValue(key, out TValue value) == false)
         {
             value = defaultValue;
         }
@@ -170,7 +153,7 @@ public static IEnumerable<XElement> LoadRuleSets(string candidatePath)
             var rulePath = Path.Combine(path, "RelaxVersioner.rules");
             if (File.Exists(rulePath))
             {
-                XElement? element = null;
+                XElement element = null;
                 try
                 {
                     element = XElement.Load(rulePath);
@@ -227,15 +210,15 @@ public static IEnumerable<Rule> AggregateRules(XElement wrules)
         return (from rule in wrules.Elements("Rule")
                 let name = rule.Attribute("name")
                 let key = rule.Attribute("key")
-                where !string.IsNullOrWhiteSpace(name?.Value) && !string.IsNullOrWhiteSpace(key?.Value)
-                select new Rule(name.Value.Trim(), key.Value.Trim(), rule.Value.Trim()));
+                where !string.IsNullOrWhiteSpace(name?.Value)
+                select new Rule(name.Value.Trim(), key?.Value.Trim(), rule.Value.Trim()));
     }
 
     public static XElement GetDefaultRuleSet()
     {
         var type = typeof(Utilities);
         using (var stream = type.Assembly.GetManifestResourceStream(
-            type, "DefaultRuleSet.rules")!)
+            type, "DefaultRuleSet.rules"))
         {
             return XElement.Load(stream);
         }
diff --git a/RelaxVersioner.Tasks/RelaxVersioner.Tasks.csproj b/RelaxVersioner.Tasks/RelaxVersioner.Tasks.csproj
index 58c0307..491d2e8 100644
--- a/RelaxVersioner.Tasks/RelaxVersioner.Tasks.csproj
+++ b/RelaxVersioner.Tasks/RelaxVersioner.Tasks.csproj
@@ -29,7 +29,7 @@
   <ItemGroup>
     <PackageReference Include="Microsoft.NETFramework.ReferenceAssemblies" Version="1.0.3" PrivateAssets="All" />
     <PackageReference Condition="'$(RV_BOOTSTRAP)' != 'True'"
-                      Include="RelaxVersioner" Version="*" PrivateAssets="all" />
+                      Include="RelaxVersioner" Version="3.2.40" PrivateAssets="all" />
   </ItemGroup>
 
 </Project>
diff --git a/RelaxVersioner/RelaxVersioner.csproj b/RelaxVersioner/RelaxVersioner.csproj
index 15c2bbd..beb7681 100644
--- a/RelaxVersioner/RelaxVersioner.csproj
+++ b/RelaxVersioner/RelaxVersioner.csproj
@@ -37,7 +37,7 @@
     <PackageReference Include="Microsoft.NETFramework.ReferenceAssemblies" Version="1.0.3" PrivateAssets="All" />
     <PackageReference Include="Mono.Options" Version="6.12.0.148" />
     <PackageReference Condition="'$(RV_BOOTSTRAP)' != 'True'"
-                      Include="RelaxVersioner" Version="*" PrivateAssets="all" />
+                      Include="RelaxVersioner" Version="3.2.40" PrivateAssets="all" />
   </ItemGroup>
 
   <ItemGroup>