icsharpcode/ILSpy · error · BadImageFormatException

Unexpected rawTypeKind

Error message

Unexpected rawTypeKind: {rawTypeKind} (0x{rawTypeKind:x})

What it means

BadImageFormatException from DisassemblerSignatureTypeProvider.GetTypeFromDefinition when the rawTypeKind byte decoded from a type signature is not one of the valid ECMA-335 codes (0x00 default, 0x11 valuetype, 0x12 class). Any other byte means corrupt signature metadata.

Solutions

1. Catch BadImageFormatException around the disassemble call and report the member as not disassemblable.
2. Verify the assembly with peverify or obtain a fresh copy; if it reproducibly fails on valid metadata, file an ILSpy issue.

try {
    disassembler.Disassemble(module, entityHandle, output);
} catch (BadImageFormatException ex) {
    logger.Warning("Corrupt signature in {Module}: {Message}", module.FileName, ex.Message);
}

When it happens

Trigger: Disassembling IL (ildasm-style output) for an assembly whose type-signature encoding contains an invalid type-kind byte: truncated, hand-edited, or obfuscated metadata.

Common situations: Corrupt PE files; IL produced by buggy or obfuscating tools; a truncated download of the assembly.

Related errors

• Expected a TypeDef, TypeRef or TypeSpec handle!
• Implementation must either be an index into the File…
• Cannot get RVA section prefix from module
• Cannot compute an ID string for an entity that is not…
• Cannot decompile this assembly to a SDK style project. Use…

AI-assisted analysis of icsharpcode/ILSpy@60c08fcb74 (2026-08-13). Data as JSON: /api/errors/53707f344d0996b3. Report an issue: GitHub.

Appendix: source

Thrown at ICSharpCode.Decompiler/Disassembler/DisassemblerSignatureTypeProvider.cs:241

				output.Write(']');
			};
		}

		public Action<ILNameSyntax> GetTypeFromDefinition(MetadataReader reader, TypeDefinitionHandle handle, byte rawTypeKind)
		{
			return syntax => {
				switch (rawTypeKind)
				{
					case 0x00:
						break;
					case 0x11:
						output.Write("valuetype ");
						break;
					case 0x12:
						output.Write("class ");
						break;
					default:
						throw new BadImageFormatException($"Unexpected rawTypeKind: {rawTypeKind} (0x{rawTypeKind:x})");
				}
				((EntityHandle)handle).WriteTo(module, output, default);
			};
		}

		public Action<ILNameSyntax> GetTypeFromReference(MetadataReader reader, TypeReferenceHandle handle, byte rawTypeKind)
		{
			return syntax => {
				switch (rawTypeKind)
				{
					case 0x00:
						break;
					case 0x11:
						output.Write("valuetype ");
						break;
					case 0x12:
						output.Write("class ");
						break;

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