diff --git a/tests/baselines/reference/promiseType.js b/tests/baselines/reference/promiseType.js
index 84d9d713b4810..8ebf72ee95bb0 100644
--- a/tests/baselines/reference/promiseType.js
+++ b/tests/baselines/reference/promiseType.js
@@ -217,6 +217,10 @@ const pc6 = p.then(() => Promise.reject("1"), () => {});
 const pc7 = p.then(() => Promise.reject("1"), () => {throw 1});
 const pc8 = p.then(() => Promise.reject("1"), () => Promise.resolve(1));
 const pc9 = p.then(() => Promise.reject("1"), () => Promise.reject(1));
+
+// #28427
+
+Promise.all([undefined as Promise<string> | number]);
 
 
 //// [promiseType.js]
@@ -440,3 +444,5 @@ const pc6 = p.then(() => Promise.reject("1"), () => { });
 const pc7 = p.then(() => Promise.reject("1"), () => { throw 1; });
 const pc8 = p.then(() => Promise.reject("1"), () => Promise.resolve(1));
 const pc9 = p.then(() => Promise.reject("1"), () => Promise.reject(1));
+// #28427
+Promise.all([undefined]);
diff --git a/tests/baselines/reference/promiseType.symbols b/tests/baselines/reference/promiseType.symbols
index cec81cd7d8266..5fdb64c8e40ec 100644
--- a/tests/baselines/reference/promiseType.symbols
+++ b/tests/baselines/reference/promiseType.symbols
@@ -1089,3 +1089,12 @@ const pc9 = p.then(() => Promise.reject("1"), () => Promise.reject(1));
 >Promise : Symbol(Promise, Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --), Decl(lib.es2015.promise.d.ts, --, --), Decl(lib.es2015.symbol.wellknown.d.ts, --, --))
 >reject : Symbol(PromiseConstructor.reject, Decl(lib.es2015.promise.d.ts, --, --))
 
+// #28427
+
+Promise.all([undefined as Promise<string> | number]);
+>Promise.all : Symbol(PromiseConstructor.all, Decl(lib.es2015.iterable.d.ts, --, --), Decl(lib.es2015.promise.d.ts, --, --))
+>Promise : Symbol(Promise, Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --), Decl(lib.es2015.promise.d.ts, --, --), Decl(lib.es2015.symbol.wellknown.d.ts, --, --))
+>all : Symbol(PromiseConstructor.all, Decl(lib.es2015.iterable.d.ts, --, --), Decl(lib.es2015.promise.d.ts, --, --))
+>undefined : Symbol(undefined)
+>Promise : Symbol(Promise, Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --), Decl(lib.es2015.promise.d.ts, --, --), Decl(lib.es2015.symbol.wellknown.d.ts, --, --))
+
diff --git a/tests/baselines/reference/promiseType.types b/tests/baselines/reference/promiseType.types
index dd20fb656ea5a..9e0ae3059a93e 100644
--- a/tests/baselines/reference/promiseType.types
+++ b/tests/baselines/reference/promiseType.types
@@ -1583,3 +1583,14 @@ const pc9 = p.then(() => Promise.reject("1"), () => Promise.reject(1));
 >reject : <T = never>(reason?: any) => Promise<T>
 >1 : 1
 
+// #28427
+
+Promise.all([undefined as Promise<string> | number]);
+>Promise.all([undefined as Promise<string> | number]) : Promise<(string | number)[]>
+>Promise.all : { <TAll>(values: Iterable<TAll>): Promise<(TAll extends PromiseLike<infer UAll> ? UAll : TAll)[]>; <T extends readonly any[]>(values: T): Promise<{ -readonly [P in keyof T]: Awaited<T[P]>; }>; }
+>Promise : PromiseConstructor
+>all : { <TAll>(values: Iterable<TAll>): Promise<(TAll extends PromiseLike<infer UAll> ? UAll : TAll)[]>; <T extends readonly any[]>(values: T): Promise<{ -readonly [P in keyof T]: Awaited<T[P]>; }>; }
+>[undefined as Promise<string> | number] : (number | Promise<string>)[]
+>undefined as Promise<string> | number : number | Promise<string>
+>undefined : undefined
+
diff --git a/tests/cases/compiler/promiseType.ts b/tests/cases/compiler/promiseType.ts
index ba4a7f6041396..efe6058044a42 100644
--- a/tests/cases/compiler/promiseType.ts
+++ b/tests/cases/compiler/promiseType.ts
@@ -217,3 +217,7 @@ const pc6 = p.then(() => Promise.reject("1"), () => {});
 const pc7 = p.then(() => Promise.reject("1"), () => {throw 1});
 const pc8 = p.then(() => Promise.reject("1"), () => Promise.resolve(1));
 const pc9 = p.then(() => Promise.reject("1"), () => Promise.reject(1));
+
+// #28427
+
+Promise.all([undefined as Promise<string> | number]);