icsharpcode/ILSpy · error · InvalidOperationException

The chosen settings require at least {minVersion}. Please ch

Error message

The chosen settings require at least {minVersion}. Please change the DecompilerSettings accordingly.

What it means

InvalidOperationException from WholeProjectDecompiler.ValidateLanguageVersion when the LanguageVersion you set is below Settings.GetMinimumRequiredVersion(). Certain DecompilerSettings flags (record classes/structs, nullable reference types, etc.) raise the minimum C# version the emitted code needs; an explicit LangVersion below that minimum cannot compile the output, so the validator rejects it.

Source

Thrown at ICSharpCode.Decompiler/CSharp/ProjectDecompiler/WholeProjectDecompiler.cs:83

		/// This is an export parameter, not decompiler state: when not set explicitly, it defaults
		/// to <see cref="DecompilerSettings.GetMinimumRequiredVersion"/> of the current settings,
		/// and an explicit value below that minimum is rejected (here and again when the export
		/// starts) because the emitted code could not compile under it.
		/// </summary>
		public LanguageVersion LanguageVersion {
			get { return languageVersion ?? Settings.GetMinimumRequiredVersion(); }
			set {
				ValidateLanguageVersion(value);
				languageVersion = value;
			}
		}

		void ValidateLanguageVersion(LanguageVersion version)
		{
			var minVersion = Settings.GetMinimumRequiredVersion();
			if (version < minVersion)
			{
				throw new InvalidOperationException($"The chosen settings require at least {minVersion}." +
					" Please change the DecompilerSettings accordingly.");
			}
		}

		bool IProjectInfoProvider.CheckForOverflowUnderflow => Settings.CheckForOverflowUnderflow;

		public IAssemblyResolver AssemblyResolver { get; }

		public IAssemblyReferenceClassifier AssemblyReferenceClassifier { get; }

		public IDebugInfoProvider? DebugInfoProvider { get; }

		/// <summary>
		/// The MSBuild ProjectGuid to use for the new project.
		/// </summary>
		public Guid ProjectGuid { get; }

		/// <summary>

View on GitHub (pinned to 60c08fcb74)

Solutions

1. Raise LanguageVersion to at least Settings.GetMinimumRequiredVersion(), or leave it unset so it defaults to that minimum.
2. Disable the DecompilerSettings flags that raised the minimum if you must target an older C#.
3. Check before assigning: var min = Settings.GetMinimumRequiredVersion(); if (desired < min) desired = min;.

Example fix

// before
settings.RecordClasses = true;
projectDecompiler.LanguageVersion = LanguageVersion.CSharp7_3; // below the raised minimum

// after
settings.RecordClasses = true;
projectDecompiler.LanguageVersion = settings.GetMinimumRequiredVersion(); // at least the required version

var min = settings.GetMinimumRequiredVersion();
if (desiredLanguageVersion < min)
    desiredLanguageVersion = min; // or disable the flags that raised the minimum
projectDecompiler.LanguageVersion = desiredLanguageVersion;

When it happens

Trigger: Setting projectDecompiler.LanguageVersion (or the export LangVersion) to an older value after enabling features whose decompiled output needs a newer C#, e.g. enabled RecordClasses (needs C# 9+) but set LanguageVersion to C# 7.3.

Common situations: Bulk-enabling DecompilerSettings flags without raising LanguageVersion; loading settings from an old config that pins LangVersion to an earlier C#.

Related errors

• Cannot use an uncached type system in the decompiler.
• Cannot decompile this assembly to a SDK style project. Use d

AI-assisted analysis of icsharpcode/ILSpy@60c08fcb74 (2026-08-13). Data as JSON: /api/errors/cab4d329d2f65d28. Report an issue: GitHub.