diff --git a/tests/baselines/reference/arrayConcat2.js b/tests/baselines/reference/arrayConcat2.js
index 8db2d62e1d357..b5f9402263238 100644
--- a/tests/baselines/reference/arrayConcat2.js
+++ b/tests/baselines/reference/arrayConcat2.js
@@ -6,6 +6,14 @@ a.concat('Hello');
 
 var b = new Array<string>();
 b.concat('hello');
+
+// #26378
+
+[1].concat(['']);
+
+// #26976
+
+[].concat([1]);
 
 
 //// [arrayConcat2.js]
@@ -14,3 +22,7 @@ a.concat("hello", 'world');
 a.concat('Hello');
 var b = new Array();
 b.concat('hello');
+// #26378
+[1].concat(['']);
+// #26976
+[].concat([1]);
diff --git a/tests/baselines/reference/arrayConcat2.symbols b/tests/baselines/reference/arrayConcat2.symbols
index 7da42f6dfcb5e..03b489dca0b2a 100644
--- a/tests/baselines/reference/arrayConcat2.symbols
+++ b/tests/baselines/reference/arrayConcat2.symbols
@@ -21,3 +21,15 @@ b.concat('hello');
 >b : Symbol(b, Decl(arrayConcat2.ts, 5, 3))
 >concat : Symbol(Array.concat, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
 
+// #26378
+
+[1].concat(['']);
+>[1].concat : Symbol(Array.concat, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+>concat : Symbol(Array.concat, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+
+// #26976
+
+[].concat([1]);
+>[].concat : Symbol(Array.concat, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+>concat : Symbol(Array.concat, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+
diff --git a/tests/baselines/reference/arrayConcat2.types b/tests/baselines/reference/arrayConcat2.types
index fc1ea6fc2b57e..3df5096fcc774 100644
--- a/tests/baselines/reference/arrayConcat2.types
+++ b/tests/baselines/reference/arrayConcat2.types
@@ -1,7 +1,7 @@
 === tests/cases/compiler/arrayConcat2.ts ===
 var a: string[] = [];
 >a : string[]
->[] : undefined[]
+>[] : never[]
 
 a.concat("hello", 'world');
 >a.concat("hello", 'world') : string[]
@@ -30,3 +30,24 @@ b.concat('hello');
 >concat : { (...items: (string | ConcatArray<string>)[]): string[]; <U>(...items: (U | ConcatArray<U>)[]): (string | U)[]; }
 >'hello' : "hello"
 
+// #26378
+
+[1].concat(['']);
+>[1].concat(['']) : (string | number)[]
+>[1].concat : { (...items: (number | ConcatArray<number>)[]): number[]; <U>(...items: (U | ConcatArray<U>)[]): (number | U)[]; }
+>[1] : number[]
+>1 : 1
+>concat : { (...items: (number | ConcatArray<number>)[]): number[]; <U>(...items: (U | ConcatArray<U>)[]): (number | U)[]; }
+>[''] : string[]
+>'' : ""
+
+// #26976
+
+[].concat([1]);
+>[].concat([1]) : number[]
+>[].concat : { (...items: ConcatArray<never>[]): never[]; <U>(...items: (U | ConcatArray<U>)[]): U[]; }
+>[] : never[]
+>concat : { (...items: ConcatArray<never>[]): never[]; <U>(...items: (U | ConcatArray<U>)[]): U[]; }
+>[1] : number[]
+>1 : 1
+
diff --git a/tests/cases/compiler/arrayConcat2.ts b/tests/cases/compiler/arrayConcat2.ts
index e69730a63a37c..a3a6918d1934e 100644
--- a/tests/cases/compiler/arrayConcat2.ts
+++ b/tests/cases/compiler/arrayConcat2.ts
@@ -5,3 +5,12 @@ a.concat('Hello');
 
 var b = new Array<string>();
 b.concat('hello');
+
+// #26378
+
+[1].concat(['']);
+
+// #26976
+
+// @strictNullChecks: true
+[].concat([1]);