Same found in my project, we have @attached(member, names: arbitrary) public macro MacroName<each U: ProtocolName>(_ name: repeat (each U).Type) = #externalMacro(module: "MacroModule", type: "MacroType") and calling it @MacroName(ImplementationOfProtocol) struct Something { ...... } class ImplementationOfProtocol: ProtocolName {} Seeing error "Expected member name or initializer call after type name"