Duplicate 'AssemblyVersion' attribute in C#

By Tan Lee Published on Mar 20, 2025 180

When you try to add the AssemblyVersion attribute to your project, for example, to auto-increment the version:

using System.Reflection;

[assembly: AssemblyVersion("1.0.0.0")]
[assembly: AssemblyFileVersion("1.0.0.0")]

You may encounter the following compiler errors:

Error CS0579: Duplicate ‘AssemblyVersion’ attribute
Error CS0579: Duplicate ‘AssemblyFileVersion’ attribute

But you don't see these attributes anywhere else in your project.

Solution

The issue arises because Visual Studio automatically generates the assembly information by default.

To disable this auto-generation, add the following to your .csproj file:

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <TargetFramework>netcoreapp3.1</TargetFramework>
  </PropertyGroup>
  <PropertyGroup>
    <GenerateAssemblyInfo>false</GenerateAssemblyInfo>
  </PropertyGroup>
</Project>

Where is the auto-generated assembly info located?

If your assembly is called DupeAssemblyVersion and you're targeting .NET Core 3.1, the auto-generated assembly info will be found at:

\obj\Debug\netcoreapp3.1\DupeAssemblyVersion.AssemblyInfo.cs

Here’s an example of what this file looks like:

//------------------------------------------------------------------------------
// <auto-generated>
//     This code was generated by a tool.
//     Runtime Version:4.0.30319.42000
//
//     Changes to this file may cause incorrect behavior and will be lost if
//     the code is regenerated.
// </auto-generated>
//------------------------------------------------------------------------------

using System;
using System.Reflection;

[assembly: System.Reflection.AssemblyCompanyAttribute("DupeAssemblyVersion")]
[assembly: System.Reflection.AssemblyConfigurationAttribute("Debug")]
[assembly: System.Reflection.AssemblyFileVersionAttribute("1.0.0.0")]
[assembly: System.Reflection.AssemblyInformationalVersionAttribute("1.0.0")]
[assembly: System.Reflection.AssemblyProductAttribute("DupeAssemblyVersion")]
[assembly: System.Reflection.AssemblyTitleAttribute("DupeAssemblyVersion")]
[assembly: System.Reflection.AssemblyVersionAttribute("1.0.0.0")]

// Generated by the MSBuild WriteCodeFragment class.

By turning off the auto-generation of assembly info, you can prevent the Duplicate ‘AssemblyVersion’ attribute error from occurring.

Tan Lee