diff --git a/src/testdir/Make_all.mak b/src/testdir/Make_all.mak
index 961718f..6b4d8df 100644
--- a/src/testdir/Make_all.mak
+++ b/src/testdir/Make_all.mak
@@ -44,7 +44,8 @@
 	test_vim9_fails \
 	test_vim9_func \
 	test_vim9_import \
-	test_vim9_script
+	test_vim9_script \
+	test_vim9_typealias
 
 TEST_VIM9_RES = \
 	test_vim9_assign.res \
@@ -56,7 +57,8 @@
 	test_vim9_fails.res \
 	test_vim9_func.res \
 	test_vim9_import.res \
-	test_vim9_script.res
+	test_vim9_script.res \
+	test_vim9_typealias.res
 
 # Benchmark scripts.
 SCRIPTS_BENCH = test_bench_regexp.res
diff --git a/src/testdir/test_vim9_script.vim b/src/testdir/test_vim9_script.vim
index f0f6ed9..b64f05e 100644
--- a/src/testdir/test_vim9_script.vim
+++ b/src/testdir/test_vim9_script.vim
@@ -4783,539 +4783,6 @@
   v9.CheckSourceSuccess(lines)
 enddef
 
-" Test for :type command to create type aliases
-def Test_typealias()
-  # Use type alias at script level
-  var lines =<< trim END
-    vim9script
-    type ListOfStrings = list<string>
-    def Foo(a: ListOfStrings): ListOfStrings
-      return a
-    enddef
-    var b: ListOfStrings = ['a', 'b']
-    assert_equal(['a', 'b'], b)
-    assert_equal(['e', 'f'], Foo(['e', 'f']))
-    assert_equal('typealias<list<string>>', typename(ListOfStrings))
-    assert_equal(v:t_typealias, type(ListOfStrings))
-    assert_equal('ListOfStrings', string(ListOfStrings))
-    assert_equal(false, null == ListOfStrings)
-  END
-  v9.CheckSourceSuccess(lines)
-
-  # Use type alias at def function level
-  lines =<< trim END
-    vim9script
-    type ListOfStrings = list<string>
-    def Foo(a: ListOfStrings): ListOfStrings
-      return a
-    enddef
-    def Bar()
-      var c: ListOfStrings = ['c', 'd']
-      assert_equal(['c', 'd'], c)
-      assert_equal(['e', 'f'], Foo(['e', 'f']))
-      assert_equal('typealias<list<string>>', typename(ListOfStrings))
-      assert_equal(v:t_typealias, type(ListOfStrings))
-      assert_equal('ListOfStrings', string(ListOfStrings))
-      assert_equal(false, null == ListOfStrings)
-    enddef
-    Bar()
-  END
-  v9.CheckSourceSuccess(lines)
-
-  # Use :type outside a Vim9 script
-  lines =<< trim END
-    type Index = number
-  END
-  v9.CheckSourceFailure(lines, 'E1393: Type can only be defined in Vim9 script', 1)
-
-  # Use :type without any arguments
-  lines =<< trim END
-    vim9script
-    type
-  END
-  v9.CheckSourceFailure(lines, 'E1397: Missing type alias name', 2)
-
-  # Use :type with a name but no type
-  lines =<< trim END
-    vim9script
-    type MyType
-  END
-  v9.CheckSourceFailure(lines, "E398: Missing '=': ", 2)
-
-  # Use :type with a name but no type following "="
-  lines =<< trim END
-    vim9script
-    type MyType =
-  END
-  v9.CheckSourceFailure(lines, 'E1398: Missing type alias type', 2)
-
-  # No space before or after "="
-  lines =<< trim END
-    vim9script
-    type MyType=number
-  END
-  v9.CheckSourceFailure(lines, 'E1315: White space required after name: MyType=number', 2)
-
-  # No space after "="
-  lines =<< trim END
-    vim9script
-    type MyType =number
-  END
-  v9.CheckSourceFailure(lines, "E1069: White space required after '=': =number", 2)
-
-  # type alias without "="
-  lines =<< trim END
-    vim9script
-    type Index number
-  END
-  v9.CheckSourceFailure(lines, "E398: Missing '=': number", 2)
-
-  # type alias for a non-existing type
-  lines =<< trim END
-    vim9script
-    type Index = integer
-  END
-  v9.CheckSourceFailure(lines, 'E1010: Type not recognized: integer', 2)
-
-  # type alias starting with lower-case letter
-  lines =<< trim END
-    vim9script
-    type index = number
-  END
-  v9.CheckSourceFailure(lines, 'E1394: Type name must start with an uppercase letter: index = number', 2)
-
-  # No white space following the alias name
-  lines =<< trim END
-    vim9script
-    type Index:number
-  END
-  v9.CheckSourceFailure(lines, 'E1315: White space required after name: Index:number', 2)
-
-  # something following the type alias
-  lines =<< trim END
-    vim9script
-    type ListOfNums = list<number> string
-  END
-  v9.CheckSourceFailure(lines, 'E488: Trailing characters:  string', 2)
-
-  # type alias name collides with a variable name
-  lines =<< trim END
-    vim9script
-    var ListOfNums: number = 10
-    type ListOfNums = list<number>
-  END
-  v9.CheckSourceFailure(lines, 'E1041: Redefining script item: "ListOfNums"', 3)
-
-  # duplicate type alias name
-  lines =<< trim END
-    vim9script
-    type MyList = list<number>
-    type MyList = list<string>
-  END
-  v9.CheckSourceFailure(lines, 'E1396: Type alias "MyList" already exists', 3)
-
-  # def function argument name collision with a type alias
-  lines =<< trim END
-    vim9script
-    type A = list<number>
-    def Foo(A: number)
-    enddef
-  END
-  v9.CheckSourceFailure(lines, 'E1168: Argument already declared in the script: A: number)', 3)
-
-  # def function local variable name collision with a type alias
-  lines =<< trim END
-    vim9script
-    type A = list<number>
-    def Foo()
-      var A: number = 10
-    enddef
-    Foo()
-  END
-  v9.CheckSourceFailure(lines, 'E1054: Variable already declared in the script: A', 1)
-
-  # type alias a variable
-  lines =<< trim END
-    vim9script
-    var A: list<number> = []
-    type B = A
-  END
-  v9.CheckSourceFailure(lines, 'E1010: Type not recognized: A', 3)
-
-  # type alias a class
-  lines =<< trim END
-    vim9script
-    class C
-    endclass
-    type AC = C
-    assert_equal('class<C>', typename(AC))
-  END
-  v9.CheckSourceSuccess(lines)
-
-  # Sourcing a script twice (which will free script local variables)
-  # Uses "lines" from the previous test
-  new
-  setline(1, lines)
-  :source
-  :source
-  bw!
-
-  # type alias a type alias
-  lines =<< trim END
-    vim9script
-    type A = string
-    type B = A
-    var b: B = 'abc'
-    assert_equal('abc', b)
-    def Foo()
-      var c: B = 'def'
-      assert_equal('def', c)
-    enddef
-    Foo()
-  END
-  v9.CheckSourceSuccess(lines)
-
-  # Assigning to a type alias (script level)
-  lines =<< trim END
-    vim9script
-    type MyType = list<number>
-    MyType = [1, 2, 3]
-  END
-  v9.CheckSourceFailure(lines, 'E1395: Type alias "MyType" cannot be modified', 3)
-
-  # Assigning a type alias (def function level)
-  lines =<< trim END
-    vim9script
-    type A = list<string>
-    def Foo()
-      var x = A
-    enddef
-    Foo()
-  END
-  v9.CheckSourceFailure(lines, 'E1403: Type alias "A" cannot be used as a value', 1)
-
-  # Using type alias in an expression (script level)
-  lines =<< trim END
-    vim9script
-    type MyType = list<number>
-    assert_fails('var m = MyType', 'E1403: Type alias "MyType" cannot be used as a value')
-    assert_fails('var i = MyType + 1', 'E1400: Using type alias "MyType" as a Number')
-    assert_fails('var f = 1.0 + MyType', 'E1400: Using type alias "MyType" as a Number')
-    assert_fails('MyType += 10', 'E1395: Type alias "MyType" cannot be modified')
-    assert_fails('var x = $"-{MyType}-"', 'E1402: Using type alias "MyType" as a String')
-    assert_fails('var x = MyType[1]', 'E909: Cannot index a special variable')
-  END
-  v9.CheckSourceSuccess(lines)
-
-  # Using type alias in an expression (def function level)
-  lines =<< trim END
-    vim9script
-    type MyType = list<number>
-    def Foo()
-      var x = MyType + 1
-    enddef
-    Foo()
-  END
-  v9.CheckSourceFailure(lines, 'E1051: Wrong argument type for +', 1)
-
-  # Using type alias in an expression (def function level)
-  lines =<< trim END
-    vim9script
-    type MyType = list<number>
-    def Foo()
-      MyType = list<string>
-    enddef
-    Foo()
-  END
-  v9.CheckSourceFailure(lines, 'E46: Cannot change read-only variable "MyType"', 1)
-
-  # Using type alias in an expression (def function level)
-  lines =<< trim END
-    vim9script
-    type MyType = list<number>
-    def Foo()
-      MyType += 10
-    enddef
-    Foo()
-  END
-  v9.CheckSourceFailure(lines, 'E46: Cannot change read-only variable "MyType"', 1)
-
-  # Convert type alias to a string (def function level)
-  lines =<< trim END
-    vim9script
-    type MyType = list<number>
-    def Foo()
-      var x = $"-{MyType}-"
-    enddef
-    Foo()
-  END
-  v9.CheckSourceFailure(lines, 'E1105: Cannot convert typealias to string', 1)
-
-  # Using type alias as a float
-  lines =<< trim END
-    vim9script
-    type B = number
-    sort([1.1, B], 'f')
-  END
-  v9.CheckSourceFailure(lines, 'E1401: Using type alias "B" as a Float', 3)
-
-  # Creating a typealias in a def function
-  lines =<< trim END
-    vim9script
-    def Foo()
-      var n: number = 10
-      type A = list<string>
-    enddef
-    defcompile
-  END
-  v9.CheckSourceFailure(lines, 'E1399: Type can only be used in a script', 2)
-
-  # json_encode should fail with a type alias
-  lines =<< trim END
-    vim9script
-    type A = list<string>
-    var x = json_encode(A)
-  END
-  v9.CheckSourceFailure(lines, 'E1161: Cannot json encode a typealias', 3)
-
-  # Comparing type alias with a number (script level)
-  lines =<< trim END
-    vim9script
-    type A = list<string>
-    var n: number
-    var x = A == n
-  END
-  v9.CheckSourceFailure(lines, 'E1072: Cannot compare typealias with number', 4)
-
-  # Comparing type alias with a number (def function level)
-  lines =<< trim END
-    vim9script
-    type A = list<string>
-    def Foo()
-      var n: number
-      var x = A == n
-    enddef
-    Foo()
-  END
-  v9.CheckSourceFailure(lines, 'E1072: Cannot compare typealias with number', 2)
-
-  # casting a number to a type alias (script level)
-  lines =<< trim END
-    vim9script
-    type MyType = bool
-    assert_equal(true, <MyType>1 == true)
-  END
-  v9.CheckSourceSuccess(lines)
-enddef
-
-" Test for exporting and importing type aliases
-def Test_typealias_import()
-  var lines =<< trim END
-    vim9script
-    export type MyType = list<number>
-  END
-  writefile(lines, 'Xtypeexport.vim', 'D')
-
-  lines =<< trim END
-    vim9script
-    import './Xtypeexport.vim' as A
-
-    var myList: A.MyType = [1, 2, 3]
-    def Foo(l: A.MyType)
-      assert_equal([1, 2, 3], l)
-    enddef
-    Foo(myList)
-  END
-  v9.CheckScriptSuccess(lines)
-
-  # Use a non existing type alias
-  lines =<< trim END
-    vim9script
-    import './Xtypeexport.vim' as A
-
-    var myNum: A.SomeType = 10
-  END
-  v9.CheckScriptFailure(lines, 'E1010: Type not recognized: A.SomeType = 10', 4)
-
-  # Use a type alias that is not exported
-  lines =<< trim END
-    vim9script
-    type NewType = dict<string>
-  END
-  writefile(lines, 'Xtypeexport2.vim', 'D')
-  lines =<< trim END
-    vim9script
-    import './Xtypeexport2.vim' as A
-
-    var myDict: A.NewType = {}
-  END
-  v9.CheckScriptFailure(lines, 'E1049: Item not exported in script: NewType', 4)
-
-  # Using the same name as an imported type alias
-  lines =<< trim END
-    vim9script
-    export type MyType2 = list<number>
-  END
-  writefile(lines, 'Xtypeexport3.vim', 'D')
-  lines =<< trim END
-    vim9script
-    import './Xtypeexport3.vim' as A
-
-    type MyType2 = A.MyType2
-    var myList1: A.MyType2 = [1, 2, 3]
-    var myList2: MyType2 = [4, 5, 6]
-    assert_equal([1, 2, 3], myList1)
-    assert_equal([4, 5, 6], myList2)
-  END
-  v9.CheckScriptSuccess(lines)
-
-  # Using an exported class to create a type alias
-  lines =<< trim END
-    vim9script
-    export class MyClass
-      this.val = 10
-    endclass
-  END
-  writefile(lines, 'Xtypeexport4.vim', 'D')
-  lines =<< trim END
-    vim9script
-    import './Xtypeexport4.vim' as T
-
-    type MyType3 = T.MyClass
-    var c: MyType3 = T.MyClass.new()
-    assert_equal(10, c.val)
-  END
-  v9.CheckScriptSuccess(lines)
-enddef
-
-" Test for using typealias as a def function argument and return type
-def Test_typealias_func_argument()
-  var lines =<< trim END
-    vim9script
-    type A = list<number>
-    def Foo(l: A): A
-      assert_equal([1, 2], l)
-      return l
-    enddef
-    var x: A = [1, 2]
-    assert_equal([1, 2], Foo(x))
-  END
-  v9.CheckScriptSuccess(lines)
-
-  # passing a type alias variable to a function expecting a specific type
-  lines =<< trim END
-    vim9script
-    type A = list<number>
-    def Foo(l: list<number>)
-      assert_equal([1, 2], l)
-    enddef
-    var x: A = [1, 2]
-    Foo(x)
-  END
-  v9.CheckScriptSuccess(lines)
-
-  # passing a type alias variable to a function expecting any
-  lines =<< trim END
-    vim9script
-    type A = list<number>
-    def Foo(l: any)
-      assert_equal([1, 2], l)
-    enddef
-    var x: A = [1, 2]
-    Foo(x)
-  END
-  v9.CheckScriptSuccess(lines)
-enddef
-
-" Using a type alias with a builtin function
-def Test_typealias_with_builtin_functions()
-  var lines =<< trim END
-    vim9script
-    type A = list<func>
-    assert_equal(0, empty(A))
-  END
-  v9.CheckScriptSuccess(lines)
-
-  # Using a type alias with len()
-  lines =<< trim END
-    vim9script
-    type A = list<func>
-    var x = len(A)
-  END
-  v9.CheckScriptFailure(lines, 'E701: Invalid type for len()', 3)
-
-  # Using a type alias with len()
-  lines =<< trim END
-    vim9script
-    type A = list<func>
-    def Foo()
-      var x = len(A)
-    enddef
-    Foo()
-  END
-  v9.CheckScriptFailure(lines, 'E1013: Argument 1: type mismatch, expected list<any> but got typealias', 1)
-
-  # Using a type alias with eval()
-  lines =<< trim END
-    vim9script
-    type A = number
-    def Foo()
-      var x = eval("A")
-    enddef
-    Foo()
-  END
-  v9.CheckScriptFailure(lines, 'E1403: Type alias "A" cannot be used as a value', 1)
-enddef
-
-" Test for type alias refcount
-def Test_typealias_refcount()
-  var lines =<< trim END
-    vim9script
-    type A = list<func>
-    assert_equal(1, test_refcount(A))
-  END
-  v9.CheckScriptSuccess(lines)
-
-  lines =<< trim END
-    vim9script
-    type B = list<number>
-    var x: B = []
-    assert_equal(1, test_refcount(B))
-  END
-  v9.CheckScriptSuccess(lines)
-enddef
-
-" Test for using instanceof() with a type alias
-def Test_typealias_instanceof()
-  var lines =<< trim END
-    vim9script
-    class C
-    endclass
-
-    type Ctype = C
-    var o = C.new()
-    assert_equal(1, instanceof(o, Ctype))
-    type Ntype = number
-    assert_fails('instanceof(o, Ntype)', 'E693: List or Class required for argument 2')
-    assert_equal(1, instanceof(o, [Ctype]))
-  END
-  v9.CheckScriptSuccess(lines)
-enddef
-
-" Test for type aliasing a class
-def Test_typealias_class()
-  var lines =<< trim END
-    vim9script
-    class C
-      this.color = 'green'
-    endclass
-    type MyClass = C
-    var o: MyClass = MyClass.new()
-    assert_equal('green', o.color)
-  END
-  v9.CheckScriptSuccess(lines)
-enddef
-
 " Keep this last, it messes up highlighting.
 def Test_substitute_cmd()
   new
diff --git a/src/testdir/test_vim9_typealias.vim b/src/testdir/test_vim9_typealias.vim
new file mode 100644
index 0000000..bb3efb8
--- /dev/null
+++ b/src/testdir/test_vim9_typealias.vim
@@ -0,0 +1,539 @@
+" Test Vim9 type aliases
+
+source check.vim
+import './vim9.vim' as v9
+
+" Test for :type command to create type aliases
+def Test_typealias()
+  # Use type alias at script level
+  var lines =<< trim END
+    vim9script
+    type ListOfStrings = list<string>
+    def Foo(a: ListOfStrings): ListOfStrings
+      return a
+    enddef
+    var b: ListOfStrings = ['a', 'b']
+    assert_equal(['a', 'b'], b)
+    assert_equal(['e', 'f'], Foo(['e', 'f']))
+    assert_equal('typealias<list<string>>', typename(ListOfStrings))
+    assert_equal(v:t_typealias, type(ListOfStrings))
+    assert_equal('ListOfStrings', string(ListOfStrings))
+    assert_equal(false, null == ListOfStrings)
+  END
+  v9.CheckSourceSuccess(lines)
+
+  # Use type alias at def function level
+  lines =<< trim END
+    vim9script
+    type ListOfStrings = list<string>
+    def Foo(a: ListOfStrings): ListOfStrings
+      return a
+    enddef
+    def Bar()
+      var c: ListOfStrings = ['c', 'd']
+      assert_equal(['c', 'd'], c)
+      assert_equal(['e', 'f'], Foo(['e', 'f']))
+      assert_equal('typealias<list<string>>', typename(ListOfStrings))
+      assert_equal(v:t_typealias, type(ListOfStrings))
+      assert_equal('ListOfStrings', string(ListOfStrings))
+      assert_equal(false, null == ListOfStrings)
+    enddef
+    Bar()
+  END
+  v9.CheckSourceSuccess(lines)
+
+  # Use :type outside a Vim9 script
+  lines =<< trim END
+    type Index = number
+  END
+  v9.CheckSourceFailure(lines, 'E1393: Type can only be defined in Vim9 script', 1)
+
+  # Use :type without any arguments
+  lines =<< trim END
+    vim9script
+    type
+  END
+  v9.CheckSourceFailure(lines, 'E1397: Missing type alias name', 2)
+
+  # Use :type with a name but no type
+  lines =<< trim END
+    vim9script
+    type MyType
+  END
+  v9.CheckSourceFailure(lines, "E398: Missing '=': ", 2)
+
+  # Use :type with a name but no type following "="
+  lines =<< trim END
+    vim9script
+    type MyType =
+  END
+  v9.CheckSourceFailure(lines, 'E1398: Missing type alias type', 2)
+
+  # No space before or after "="
+  lines =<< trim END
+    vim9script
+    type MyType=number
+  END
+  v9.CheckSourceFailure(lines, 'E1315: White space required after name: MyType=number', 2)
+
+  # No space after "="
+  lines =<< trim END
+    vim9script
+    type MyType =number
+  END
+  v9.CheckSourceFailure(lines, "E1069: White space required after '=': =number", 2)
+
+  # type alias without "="
+  lines =<< trim END
+    vim9script
+    type Index number
+  END
+  v9.CheckSourceFailure(lines, "E398: Missing '=': number", 2)
+
+  # type alias for a non-existing type
+  lines =<< trim END
+    vim9script
+    type Index = integer
+  END
+  v9.CheckSourceFailure(lines, 'E1010: Type not recognized: integer', 2)
+
+  # type alias starting with lower-case letter
+  lines =<< trim END
+    vim9script
+    type index = number
+  END
+  v9.CheckSourceFailure(lines, 'E1394: Type name must start with an uppercase letter: index = number', 2)
+
+  # No white space following the alias name
+  lines =<< trim END
+    vim9script
+    type Index:number
+  END
+  v9.CheckSourceFailure(lines, 'E1315: White space required after name: Index:number', 2)
+
+  # something following the type alias
+  lines =<< trim END
+    vim9script
+    type ListOfNums = list<number> string
+  END
+  v9.CheckSourceFailure(lines, 'E488: Trailing characters:  string', 2)
+
+  # type alias name collides with a variable name
+  lines =<< trim END
+    vim9script
+    var ListOfNums: number = 10
+    type ListOfNums = list<number>
+  END
+  v9.CheckSourceFailure(lines, 'E1041: Redefining script item: "ListOfNums"', 3)
+
+  # duplicate type alias name
+  lines =<< trim END
+    vim9script
+    type MyList = list<number>
+    type MyList = list<string>
+  END
+  v9.CheckSourceFailure(lines, 'E1396: Type alias "MyList" already exists', 3)
+
+  # def function argument name collision with a type alias
+  lines =<< trim END
+    vim9script
+    type A = list<number>
+    def Foo(A: number)
+    enddef
+  END
+  v9.CheckSourceFailure(lines, 'E1168: Argument already declared in the script: A: number)', 3)
+
+  # def function local variable name collision with a type alias
+  lines =<< trim END
+    vim9script
+    type A = list<number>
+    def Foo()
+      var A: number = 10
+    enddef
+    Foo()
+  END
+  v9.CheckSourceFailure(lines, 'E1054: Variable already declared in the script: A', 1)
+
+  # type alias a variable
+  lines =<< trim END
+    vim9script
+    var A: list<number> = []
+    type B = A
+  END
+  v9.CheckSourceFailure(lines, 'E1010: Type not recognized: A', 3)
+
+  # type alias a class
+  lines =<< trim END
+    vim9script
+    class C
+    endclass
+    type AC = C
+    assert_equal('class<C>', typename(AC))
+  END
+  v9.CheckSourceSuccess(lines)
+
+  # Sourcing a script twice (which will free script local variables)
+  # Uses "lines" from the previous test
+  new
+  setline(1, lines)
+  :source
+  :source
+  bw!
+
+  # type alias a type alias
+  lines =<< trim END
+    vim9script
+    type A = string
+    type B = A
+    var b: B = 'abc'
+    assert_equal('abc', b)
+    def Foo()
+      var c: B = 'def'
+      assert_equal('def', c)
+    enddef
+    Foo()
+  END
+  v9.CheckSourceSuccess(lines)
+
+  # Assigning to a type alias (script level)
+  lines =<< trim END
+    vim9script
+    type MyType = list<number>
+    MyType = [1, 2, 3]
+  END
+  v9.CheckSourceFailure(lines, 'E1395: Type alias "MyType" cannot be modified', 3)
+
+  # Assigning a type alias (def function level)
+  lines =<< trim END
+    vim9script
+    type A = list<string>
+    def Foo()
+      var x = A
+    enddef
+    Foo()
+  END
+  v9.CheckSourceFailure(lines, 'E1403: Type alias "A" cannot be used as a value', 1)
+
+  # Using type alias in an expression (script level)
+  lines =<< trim END
+    vim9script
+    type MyType = list<number>
+    assert_fails('var m = MyType', 'E1403: Type alias "MyType" cannot be used as a value')
+    assert_fails('var i = MyType + 1', 'E1400: Using type alias "MyType" as a Number')
+    assert_fails('var f = 1.0 + MyType', 'E1400: Using type alias "MyType" as a Number')
+    assert_fails('MyType += 10', 'E1395: Type alias "MyType" cannot be modified')
+    assert_fails('var x = $"-{MyType}-"', 'E1402: Using type alias "MyType" as a String')
+    assert_fails('var x = MyType[1]', 'E909: Cannot index a special variable')
+  END
+  v9.CheckSourceSuccess(lines)
+
+  # Using type alias in an expression (def function level)
+  lines =<< trim END
+    vim9script
+    type MyType = list<number>
+    def Foo()
+      var x = MyType + 1
+    enddef
+    Foo()
+  END
+  v9.CheckSourceFailure(lines, 'E1051: Wrong argument type for +', 1)
+
+  # Using type alias in an expression (def function level)
+  lines =<< trim END
+    vim9script
+    type MyType = list<number>
+    def Foo()
+      MyType = list<string>
+    enddef
+    Foo()
+  END
+  v9.CheckSourceFailure(lines, 'E46: Cannot change read-only variable "MyType"', 1)
+
+  # Using type alias in an expression (def function level)
+  lines =<< trim END
+    vim9script
+    type MyType = list<number>
+    def Foo()
+      MyType += 10
+    enddef
+    Foo()
+  END
+  v9.CheckSourceFailure(lines, 'E46: Cannot change read-only variable "MyType"', 1)
+
+  # Convert type alias to a string (def function level)
+  lines =<< trim END
+    vim9script
+    type MyType = list<number>
+    def Foo()
+      var x = $"-{MyType}-"
+    enddef
+    Foo()
+  END
+  v9.CheckSourceFailure(lines, 'E1105: Cannot convert typealias to string', 1)
+
+  # Using type alias as a float
+  lines =<< trim END
+    vim9script
+    type B = number
+    sort([1.1, B], 'f')
+  END
+  v9.CheckSourceFailure(lines, 'E1401: Using type alias "B" as a Float', 3)
+
+  # Creating a typealias in a def function
+  lines =<< trim END
+    vim9script
+    def Foo()
+      var n: number = 10
+      type A = list<string>
+    enddef
+    defcompile
+  END
+  v9.CheckSourceFailure(lines, 'E1399: Type can only be used in a script', 2)
+
+  # json_encode should fail with a type alias
+  lines =<< trim END
+    vim9script
+    type A = list<string>
+    var x = json_encode(A)
+  END
+  v9.CheckSourceFailure(lines, 'E1161: Cannot json encode a typealias', 3)
+
+  # Comparing type alias with a number (script level)
+  lines =<< trim END
+    vim9script
+    type A = list<string>
+    var n: number
+    var x = A == n
+  END
+  v9.CheckSourceFailure(lines, 'E1072: Cannot compare typealias with number', 4)
+
+  # Comparing type alias with a number (def function level)
+  lines =<< trim END
+    vim9script
+    type A = list<string>
+    def Foo()
+      var n: number
+      var x = A == n
+    enddef
+    Foo()
+  END
+  v9.CheckSourceFailure(lines, 'E1072: Cannot compare typealias with number', 2)
+
+  # casting a number to a type alias (script level)
+  lines =<< trim END
+    vim9script
+    type MyType = bool
+    assert_equal(true, <MyType>1 == true)
+  END
+  v9.CheckSourceSuccess(lines)
+enddef
+
+" Test for exporting and importing type aliases
+def Test_typealias_import()
+  var lines =<< trim END
+    vim9script
+    export type MyType = list<number>
+  END
+  writefile(lines, 'Xtypeexport.vim', 'D')
+
+  lines =<< trim END
+    vim9script
+    import './Xtypeexport.vim' as A
+
+    var myList: A.MyType = [1, 2, 3]
+    def Foo(l: A.MyType)
+      assert_equal([1, 2, 3], l)
+    enddef
+    Foo(myList)
+  END
+  v9.CheckScriptSuccess(lines)
+
+  # Use a non existing type alias
+  lines =<< trim END
+    vim9script
+    import './Xtypeexport.vim' as A
+
+    var myNum: A.SomeType = 10
+  END
+  v9.CheckScriptFailure(lines, 'E1010: Type not recognized: A.SomeType = 10', 4)
+
+  # Use a type alias that is not exported
+  lines =<< trim END
+    vim9script
+    type NewType = dict<string>
+  END
+  writefile(lines, 'Xtypeexport2.vim', 'D')
+  lines =<< trim END
+    vim9script
+    import './Xtypeexport2.vim' as A
+
+    var myDict: A.NewType = {}
+  END
+  v9.CheckScriptFailure(lines, 'E1049: Item not exported in script: NewType', 4)
+
+  # Using the same name as an imported type alias
+  lines =<< trim END
+    vim9script
+    export type MyType2 = list<number>
+  END
+  writefile(lines, 'Xtypeexport3.vim', 'D')
+  lines =<< trim END
+    vim9script
+    import './Xtypeexport3.vim' as A
+
+    type MyType2 = A.MyType2
+    var myList1: A.MyType2 = [1, 2, 3]
+    var myList2: MyType2 = [4, 5, 6]
+    assert_equal([1, 2, 3], myList1)
+    assert_equal([4, 5, 6], myList2)
+  END
+  v9.CheckScriptSuccess(lines)
+
+  # Using an exported class to create a type alias
+  lines =<< trim END
+    vim9script
+    export class MyClass
+      this.val = 10
+    endclass
+  END
+  writefile(lines, 'Xtypeexport4.vim', 'D')
+  lines =<< trim END
+    vim9script
+    import './Xtypeexport4.vim' as T
+
+    type MyType3 = T.MyClass
+    var c: MyType3 = MyType3.new()
+    assert_equal(10, c.val)
+  END
+  v9.CheckScriptSuccess(lines)
+enddef
+
+" Test for using typealias as a def function argument and return type
+def Test_typealias_func_argument()
+  var lines =<< trim END
+    vim9script
+    type A = list<number>
+    def Foo(l: A): A
+      assert_equal([1, 2], l)
+      return l
+    enddef
+    var x: A = [1, 2]
+    assert_equal([1, 2], Foo(x))
+  END
+  v9.CheckScriptSuccess(lines)
+
+  # passing a type alias variable to a function expecting a specific type
+  lines =<< trim END
+    vim9script
+    type A = list<number>
+    def Foo(l: list<number>)
+      assert_equal([1, 2], l)
+    enddef
+    var x: A = [1, 2]
+    Foo(x)
+  END
+  v9.CheckScriptSuccess(lines)
+
+  # passing a type alias variable to a function expecting any
+  lines =<< trim END
+    vim9script
+    type A = list<number>
+    def Foo(l: any)
+      assert_equal([1, 2], l)
+    enddef
+    var x: A = [1, 2]
+    Foo(x)
+  END
+  v9.CheckScriptSuccess(lines)
+enddef
+
+" Using a type alias with a builtin function
+def Test_typealias_with_builtin_functions()
+  var lines =<< trim END
+    vim9script
+    type A = list<func>
+    assert_equal(0, empty(A))
+  END
+  v9.CheckScriptSuccess(lines)
+
+  # Using a type alias with len()
+  lines =<< trim END
+    vim9script
+    type A = list<func>
+    var x = len(A)
+  END
+  v9.CheckScriptFailure(lines, 'E701: Invalid type for len()', 3)
+
+  # Using a type alias with len()
+  lines =<< trim END
+    vim9script
+    type A = list<func>
+    def Foo()
+      var x = len(A)
+    enddef
+    Foo()
+  END
+  v9.CheckScriptFailure(lines, 'E1013: Argument 1: type mismatch, expected list<any> but got typealias', 1)
+
+  # Using a type alias with eval()
+  lines =<< trim END
+    vim9script
+    type A = number
+    def Foo()
+      var x = eval("A")
+    enddef
+    Foo()
+  END
+  v9.CheckScriptFailure(lines, 'E1403: Type alias "A" cannot be used as a value', 1)
+enddef
+
+" Test for type alias refcount
+def Test_typealias_refcount()
+  var lines =<< trim END
+    vim9script
+    type A = list<func>
+    assert_equal(1, test_refcount(A))
+  END
+  v9.CheckScriptSuccess(lines)
+
+  lines =<< trim END
+    vim9script
+    type B = list<number>
+    var x: B = []
+    assert_equal(1, test_refcount(B))
+  END
+  v9.CheckScriptSuccess(lines)
+enddef
+
+" Test for using instanceof() with a type alias
+def Test_typealias_instanceof()
+  var lines =<< trim END
+    vim9script
+    class C
+    endclass
+
+    type Ctype = C
+    var o = C.new()
+    assert_equal(1, instanceof(o, Ctype))
+    type Ntype = number
+    assert_fails('instanceof(o, Ntype)', 'E693: List or Class required for argument 2')
+    assert_equal(1, instanceof(o, [Ctype]))
+  END
+  v9.CheckScriptSuccess(lines)
+enddef
+
+" Test for type aliasing a class
+def Test_typealias_class()
+  var lines =<< trim END
+    vim9script
+    class C
+      this.color = 'green'
+    endclass
+    type MyClass = C
+    var o: MyClass = MyClass.new()
+    assert_equal('green', o.color)
+  END
+  v9.CheckScriptSuccess(lines)
+enddef
+
+" vim: ts=8 sw=2 sts=2 expandtab tw=80 fdm=marker
diff --git a/src/version.c b/src/version.c
index fdfdf3f..a75c4a6 100644
--- a/src/version.c
+++ b/src/version.c
@@ -705,6 +705,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    2080,
+/**/
     2079,
 /**/
     2078,