diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 0f2b62bf4937c..474f062c9da6e 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -17034,7 +17034,7 @@ namespace ts {
         function instantiateMappedTupleType(tupleType: TupleTypeReference, mappedType: MappedType, mapper: TypeMapper) {
             const elementFlags = tupleType.target.elementFlags;
             const elementTypes = map(getTypeArguments(tupleType), (_, i) =>
-                instantiateMappedTypeTemplate(mappedType, getStringLiteralType("" + i), !!(elementFlags[i] & ElementFlags.Optional), mapper));
+                instantiateMappedTypeTemplate(mappedType, getNumberLiteralType(i), !!(elementFlags[i] & ElementFlags.Optional), mapper));
             const modifiers = getMappedTypeModifiers(mappedType);
             const newTupleModifiers = modifiers & MappedTypeModifiers.IncludeOptional ? map(elementFlags, f => f & ElementFlags.Required ? ElementFlags.Optional : f) :
                 modifiers & MappedTypeModifiers.ExcludeOptional ? map(elementFlags, f => f & ElementFlags.Optional ? ElementFlags.Required : f) :
diff --git a/tests/baselines/reference/mappedTypeTupleTypePropType.js b/tests/baselines/reference/mappedTypeTupleTypePropType.js
new file mode 100644
index 0000000000000..d0cb6685c84c8
--- /dev/null
+++ b/tests/baselines/reference/mappedTypeTupleTypePropType.js
@@ -0,0 +1,40 @@
+//// [mappedTypeTupleTypePropType.ts]
+type Indices<T extends Array<any>> = {
+  [K in keyof T]: K
+};
+
+// should contain numbers
+type MyIndices = Indices<[string, number]>;
+// union of indices should be preserved
+type StillMyIndices = MyIndices[number] & number
+
+// simplified repro from https://twitter.com/oleg008/status/1508422774401949704
+
+type Container<V> = {
+  value: V;
+};
+
+type UnwrapContainers<T extends Container<unknown>[]> = {
+  [K in keyof T]: T[K & number]["value"];
+};
+
+declare function combine<T extends Container<unknown>[]>(
+  containers: [...T],
+  callback: (...values: UnwrapContainers<T>) => void
+): void;
+
+declare const container1: Container<string>;
+declare const container2: Container<number>;
+
+combine([container1, container2], (value1, value2) => {
+  const val1: string = value1;
+  const val2: number = value2;
+});
+
+
+
+//// [mappedTypeTupleTypePropType.js]
+combine([container1, container2], function (value1, value2) {
+    var val1 = value1;
+    var val2 = value2;
+});
diff --git a/tests/baselines/reference/mappedTypeTupleTypePropType.symbols b/tests/baselines/reference/mappedTypeTupleTypePropType.symbols
new file mode 100644
index 0000000000000..3971a27f71450
--- /dev/null
+++ b/tests/baselines/reference/mappedTypeTupleTypePropType.symbols
@@ -0,0 +1,91 @@
+=== tests/cases/compiler/mappedTypeTupleTypePropType.ts ===
+type Indices<T extends Array<any>> = {
+>Indices : Symbol(Indices, Decl(mappedTypeTupleTypePropType.ts, 0, 0))
+>T : Symbol(T, Decl(mappedTypeTupleTypePropType.ts, 0, 13))
+>Array : Symbol(Array, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+
+  [K in keyof T]: K
+>K : Symbol(K, Decl(mappedTypeTupleTypePropType.ts, 1, 3))
+>T : Symbol(T, Decl(mappedTypeTupleTypePropType.ts, 0, 13))
+>K : Symbol(K, Decl(mappedTypeTupleTypePropType.ts, 1, 3))
+
+};
+
+// should contain numbers
+type MyIndices = Indices<[string, number]>;
+>MyIndices : Symbol(MyIndices, Decl(mappedTypeTupleTypePropType.ts, 2, 2))
+>Indices : Symbol(Indices, Decl(mappedTypeTupleTypePropType.ts, 0, 0))
+
+// union of indices should be preserved
+type StillMyIndices = MyIndices[number] & number
+>StillMyIndices : Symbol(StillMyIndices, Decl(mappedTypeTupleTypePropType.ts, 5, 43))
+>MyIndices : Symbol(MyIndices, Decl(mappedTypeTupleTypePropType.ts, 2, 2))
+
+// simplified repro from https://twitter.com/oleg008/status/1508422774401949704
+
+type Container<V> = {
+>Container : Symbol(Container, Decl(mappedTypeTupleTypePropType.ts, 7, 48))
+>V : Symbol(V, Decl(mappedTypeTupleTypePropType.ts, 11, 15))
+
+  value: V;
+>value : Symbol(value, Decl(mappedTypeTupleTypePropType.ts, 11, 21))
+>V : Symbol(V, Decl(mappedTypeTupleTypePropType.ts, 11, 15))
+
+};
+
+type UnwrapContainers<T extends Container<unknown>[]> = {
+>UnwrapContainers : Symbol(UnwrapContainers, Decl(mappedTypeTupleTypePropType.ts, 13, 2))
+>T : Symbol(T, Decl(mappedTypeTupleTypePropType.ts, 15, 22))
+>Container : Symbol(Container, Decl(mappedTypeTupleTypePropType.ts, 7, 48))
+
+  [K in keyof T]: T[K & number]["value"];
+>K : Symbol(K, Decl(mappedTypeTupleTypePropType.ts, 16, 3))
+>T : Symbol(T, Decl(mappedTypeTupleTypePropType.ts, 15, 22))
+>T : Symbol(T, Decl(mappedTypeTupleTypePropType.ts, 15, 22))
+>K : Symbol(K, Decl(mappedTypeTupleTypePropType.ts, 16, 3))
+
+};
+
+declare function combine<T extends Container<unknown>[]>(
+>combine : Symbol(combine, Decl(mappedTypeTupleTypePropType.ts, 17, 2))
+>T : Symbol(T, Decl(mappedTypeTupleTypePropType.ts, 19, 25))
+>Container : Symbol(Container, Decl(mappedTypeTupleTypePropType.ts, 7, 48))
+
+  containers: [...T],
+>containers : Symbol(containers, Decl(mappedTypeTupleTypePropType.ts, 19, 57))
+>T : Symbol(T, Decl(mappedTypeTupleTypePropType.ts, 19, 25))
+
+  callback: (...values: UnwrapContainers<T>) => void
+>callback : Symbol(callback, Decl(mappedTypeTupleTypePropType.ts, 20, 21))
+>values : Symbol(values, Decl(mappedTypeTupleTypePropType.ts, 21, 13))
+>UnwrapContainers : Symbol(UnwrapContainers, Decl(mappedTypeTupleTypePropType.ts, 13, 2))
+>T : Symbol(T, Decl(mappedTypeTupleTypePropType.ts, 19, 25))
+
+): void;
+
+declare const container1: Container<string>;
+>container1 : Symbol(container1, Decl(mappedTypeTupleTypePropType.ts, 24, 13))
+>Container : Symbol(Container, Decl(mappedTypeTupleTypePropType.ts, 7, 48))
+
+declare const container2: Container<number>;
+>container2 : Symbol(container2, Decl(mappedTypeTupleTypePropType.ts, 25, 13))
+>Container : Symbol(Container, Decl(mappedTypeTupleTypePropType.ts, 7, 48))
+
+combine([container1, container2], (value1, value2) => {
+>combine : Symbol(combine, Decl(mappedTypeTupleTypePropType.ts, 17, 2))
+>container1 : Symbol(container1, Decl(mappedTypeTupleTypePropType.ts, 24, 13))
+>container2 : Symbol(container2, Decl(mappedTypeTupleTypePropType.ts, 25, 13))
+>value1 : Symbol(value1, Decl(mappedTypeTupleTypePropType.ts, 27, 35))
+>value2 : Symbol(value2, Decl(mappedTypeTupleTypePropType.ts, 27, 42))
+
+  const val1: string = value1;
+>val1 : Symbol(val1, Decl(mappedTypeTupleTypePropType.ts, 28, 7))
+>value1 : Symbol(value1, Decl(mappedTypeTupleTypePropType.ts, 27, 35))
+
+  const val2: number = value2;
+>val2 : Symbol(val2, Decl(mappedTypeTupleTypePropType.ts, 29, 7))
+>value2 : Symbol(value2, Decl(mappedTypeTupleTypePropType.ts, 27, 42))
+
+});
+
+
diff --git a/tests/baselines/reference/mappedTypeTupleTypePropType.types b/tests/baselines/reference/mappedTypeTupleTypePropType.types
new file mode 100644
index 0000000000000..ebd0a26a6833b
--- /dev/null
+++ b/tests/baselines/reference/mappedTypeTupleTypePropType.types
@@ -0,0 +1,70 @@
+=== tests/cases/compiler/mappedTypeTupleTypePropType.ts ===
+type Indices<T extends Array<any>> = {
+>Indices : Indices<T>
+
+  [K in keyof T]: K
+};
+
+// should contain numbers
+type MyIndices = Indices<[string, number]>;
+>MyIndices : [0, 1]
+
+// union of indices should be preserved
+type StillMyIndices = MyIndices[number] & number
+>StillMyIndices : StillMyIndices
+
+// simplified repro from https://twitter.com/oleg008/status/1508422774401949704
+
+type Container<V> = {
+>Container : Container<V>
+
+  value: V;
+>value : V
+
+};
+
+type UnwrapContainers<T extends Container<unknown>[]> = {
+>UnwrapContainers : UnwrapContainers<T>
+
+  [K in keyof T]: T[K & number]["value"];
+};
+
+declare function combine<T extends Container<unknown>[]>(
+>combine : <T extends Container<unknown>[]>(containers: [...T], callback: (...values: UnwrapContainers<T>) => void) => void
+
+  containers: [...T],
+>containers : [...T]
+
+  callback: (...values: UnwrapContainers<T>) => void
+>callback : (...values: UnwrapContainers<T>) => void
+>values : UnwrapContainers<T>
+
+): void;
+
+declare const container1: Container<string>;
+>container1 : Container<string>
+
+declare const container2: Container<number>;
+>container2 : Container<number>
+
+combine([container1, container2], (value1, value2) => {
+>combine([container1, container2], (value1, value2) => {  const val1: string = value1;  const val2: number = value2;}) : void
+>combine : <T extends Container<unknown>[]>(containers: [...T], callback: (...values: UnwrapContainers<T>) => void) => void
+>[container1, container2] : [Container<string>, Container<number>]
+>container1 : Container<string>
+>container2 : Container<number>
+>(value1, value2) => {  const val1: string = value1;  const val2: number = value2;} : (value1: string, value2: number) => void
+>value1 : string
+>value2 : number
+
+  const val1: string = value1;
+>val1 : string
+>value1 : string
+
+  const val2: number = value2;
+>val2 : number
+>value2 : number
+
+});
+
+
diff --git a/tests/cases/compiler/mappedTypeTupleTypePropType.ts b/tests/cases/compiler/mappedTypeTupleTypePropType.ts
new file mode 100644
index 0000000000000..9dea1d773fcba
--- /dev/null
+++ b/tests/cases/compiler/mappedTypeTupleTypePropType.ts
@@ -0,0 +1,32 @@
+type Indices<T extends Array<any>> = {
+  [K in keyof T]: K
+};
+
+// should contain numbers
+type MyIndices = Indices<[string, number]>;
+// union of indices should be preserved
+type StillMyIndices = MyIndices[number] & number
+
+// simplified repro from https://twitter.com/oleg008/status/1508422774401949704
+
+type Container<V> = {
+  value: V;
+};
+
+type UnwrapContainers<T extends Container<unknown>[]> = {
+  [K in keyof T]: T[K & number]["value"];
+};
+
+declare function combine<T extends Container<unknown>[]>(
+  containers: [...T],
+  callback: (...values: UnwrapContainers<T>) => void
+): void;
+
+declare const container1: Container<string>;
+declare const container2: Container<number>;
+
+combine([container1, container2], (value1, value2) => {
+  const val1: string = value1;
+  const val2: number = value2;
+});
+