tests/cases/compiler/objectLiteralIndexerErrors.ts(13,5): error TS2322: Type '{ [x: string]: A; [x: number]: A; 0: A; x: B; }' is not assignable to type '{ [s: string]: A; [n: number]: B; }'. Index signatures are incompatible. Type 'A' is not assignable to type 'B'. ==== tests/cases/compiler/objectLiteralIndexerErrors.ts (1 errors) ==== interface A { x: number; } interface B extends A { y: string; } var a: A; var b: B; var c: any; var o1: { [s: string]: A;[n: number]: B; } = { x: b, 0: a }; // both indexers are A ~~ !!! error TS2322: Type '{ [x: string]: A; [x: number]: A; 0: A; x: B; }' is not assignable to type '{ [s: string]: A; [n: number]: B; }'. !!! error TS2322: Index signatures are incompatible. !!! error TS2322: Type 'A' is not assignable to type 'B'. o1 = { x: c, 0: a }; // string indexer is any, number indexer is A