diff --git a/Directory.Build.props b/Directory.Build.props
index 8d29f4085..a042e9147 100644
--- a/Directory.Build.props
+++ b/Directory.Build.props
@@ -3,6 +3,13 @@
     <NoWarn>$(NoWarn);NU1510</NoWarn>
   </PropertyGroup>
 
+  <PropertyGroup>
+    <!-- Warnings are errors repo-wide so a clean build stays clean; individual projects can opt
+         back out (e.g. ICSharpCode.ILSpyCmd sets TreatWarningsAsErrors=false) since project-level
+         properties override this imported default. -->
+    <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
+  </PropertyGroup>
+
   <PropertyGroup>
     <EnableNUnitRunner>true</EnableNUnitRunner>
   </PropertyGroup>
diff --git a/ILSpy.AddIn.VS2022/ILSpy.AddIn.VS2022.csproj b/ILSpy.AddIn.VS2022/ILSpy.AddIn.VS2022.csproj
index dcea51027..9d89f674e 100644
--- a/ILSpy.AddIn.VS2022/ILSpy.AddIn.VS2022.csproj
+++ b/ILSpy.AddIn.VS2022/ILSpy.AddIn.VS2022.csproj
@@ -11,6 +11,8 @@
     <Version>1.7.1.0</Version>
     <FileVersion>1.7.1.0</FileVersion>
     <LangVersion>9.0</LangVersion>
+    <!-- Legacy net472 add-in: opt out of the repo-wide warnings-as-errors (Directory.Build.props). -->
+    <TreatWarningsAsErrors>false</TreatWarningsAsErrors>
 
     <EnableDefaultItems>False</EnableDefaultItems>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
diff --git a/ILSpy.AddIn/ILSpy.AddIn.csproj b/ILSpy.AddIn/ILSpy.AddIn.csproj
index 3681515de..db5f3114e 100644
--- a/ILSpy.AddIn/ILSpy.AddIn.csproj
+++ b/ILSpy.AddIn/ILSpy.AddIn.csproj
@@ -11,6 +11,8 @@
     <Version>1.7.1.0</Version>
     <FileVersion>1.7.1.0</FileVersion>
     <LangVersion>9.0</LangVersion>
+    <!-- Legacy net472 add-in: opt out of the repo-wide warnings-as-errors (Directory.Build.props). -->
+    <TreatWarningsAsErrors>false</TreatWarningsAsErrors>
 
     <EnableDefaultItems>False</EnableDefaultItems>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
diff --git a/ILSpy.Installer/ILSpy.Installer.csproj b/ILSpy.Installer/ILSpy.Installer.csproj
index 8603eb6f1..51dae3d0f 100644
--- a/ILSpy.Installer/ILSpy.Installer.csproj
+++ b/ILSpy.Installer/ILSpy.Installer.csproj
@@ -4,6 +4,8 @@
     <OutputType>Exe</OutputType>
     <TargetFramework>net472</TargetFramework>
     <StartupObject>ILSpy.Installer.Builder</StartupObject>
+    <!-- Legacy net472 installer builder: opt out of the repo-wide warnings-as-errors (Directory.Build.props). -->
+    <TreatWarningsAsErrors>false</TreatWarningsAsErrors>
   </PropertyGroup>
 
   <PropertyGroup>