diff --git a/src/testdir/test_vim9_assign.vim b/src/testdir/test_vim9_assign.vim
index 8be0769..e288d03 100644
--- a/src/testdir/test_vim9_assign.vim
+++ b/src/testdir/test_vim9_assign.vim
@@ -3064,7 +3064,7 @@
     endclass
     class D
     endclass
-    assert_fails('C = D', 'E1403: Class "D" cannot be used as a value')
+    assert_fails('C = D', 'E1405: Class "D" cannot be used as a value')
   END
   v9.CheckSourceSuccess(lines)
 enddef
@@ -3105,7 +3105,7 @@
     assert_fails('N = l', 'E1012: Type mismatch; expected number but got list<number>')
     assert_fails('N = b', 'E1012: Type mismatch; expected number but got blob')
     assert_fails('N = Fn', 'E1012: Type mismatch; expected number but got func([unknown]): number')
-    assert_fails('N = A', 'E1403: Class "A" cannot be used as a value')
+    assert_fails('N = A', 'E1405: Class "A" cannot be used as a value')
     assert_fails('N = o', 'E1012: Type mismatch; expected number but got object<A>')
 
     # Use a compound operator with different RHS types
@@ -3113,7 +3113,7 @@
     assert_fails('N += l', 'E734: Wrong variable type for +=')
     assert_fails('N += b', 'E974: Using a Blob as a Number')
     assert_fails('N += Fn', 'E734: Wrong variable type for +=')
-    assert_fails('N += A', 'E1403: Class "A" cannot be used as a value')
+    assert_fails('N += A', 'E1405: Class "A" cannot be used as a value')
     assert_fails('N += o', 'E1320: Using an Object as a Number')
 
     # Initialize multiple variables using []
@@ -3121,7 +3121,7 @@
     assert_fails('var [X2: number, Y: number] = [1, l]', 'E1012: Type mismatch; expected number but got list<number>')
     assert_fails('var [X3: number, Y: number] = [1, b]', 'E1012: Type mismatch; expected number but got blob')
     assert_fails('var [X4: number, Y: number] = [1, Fn]', 'E1012: Type mismatch; expected number but got func([unknown]): number')
-    assert_fails('var [X7: number, Y: number] = [1, A]', 'E1403: Class "A" cannot be used as a value')
+    assert_fails('var [X7: number, Y: number] = [1, A]', 'E1405: Class "A" cannot be used as a value')
     assert_fails('var [X8: number, Y: number] = [1, o]', 'E1012: Type mismatch; expected number but got object<A>')
 
     # String concatenation with various LHS types
@@ -3129,7 +3129,7 @@
     assert_fails('S ..= l', 'E734: Wrong variable type for .=')
     assert_fails('S ..= b', 'E976: Using a Blob as a String')
     assert_fails('S ..= Fn', 'E734: Wrong variable type for .=')
-    assert_fails('S ..= A', 'E1403: Class "A" cannot be used as a value')
+    assert_fails('S ..= A', 'E1405: Class "A" cannot be used as a value')
     assert_fails('S ..= o', 'E1324: Using an Object as a String')
 
     # String concatenation with various RHS types
diff --git a/src/testdir/test_vim9_builtin.vim b/src/testdir/test_vim9_builtin.vim
index f9d2e41..216118e 100644
--- a/src/testdir/test_vim9_builtin.vim
+++ b/src/testdir/test_vim9_builtin.vim
@@ -2316,7 +2316,7 @@
     endclass
     instanceof(Foo.new(), 123)
   END
-  v9.CheckScriptFailure(lines, 'E693: List or Class required for argument 2')
+  v9.CheckScriptFailure(lines, 'E693: Class or class typealias required for argument 2')
 
   lines =<< trim END
     vim9script
@@ -2338,7 +2338,7 @@
     enddef
     Bar()
   END
-  v9.CheckScriptFailure(lines, 'E1013: Argument 2: type mismatch, expected class<Unknown> but got number')
+  v9.CheckScriptFailure(lines, 'E693: Class or class typealias required for argument 2')
 
   lines =<< trim END
     vim9script
@@ -2346,7 +2346,7 @@
     endclass
     instanceof(Foo.new(), [{}])
   END
-  v9.CheckSourceFailure(lines, 'E614: Class required')
+  v9.CheckSourceFailure(lines, 'E693: Class or class typealias required for argument 2')
 
   lines =<< trim END
     vim9script
@@ -2357,7 +2357,7 @@
     enddef
     Bar()
   END
-  v9.CheckSourceFailure(lines, 'E614: Class required')
+  v9.CheckSourceFailure(lines, 'E693: Class or class typealias required for argument 2')
 enddef
 
 def Test_invert()
diff --git a/src/testdir/test_vim9_class.vim b/src/testdir/test_vim9_class.vim
index 84ea1cb..e0f5db6 100644
--- a/src/testdir/test_vim9_class.vim
+++ b/src/testdir/test_vim9_class.vim
@@ -3328,6 +3328,11 @@
     class Base3 extends Mix1
     endclass
 
+    type AliasBase1 = Base1
+    type AliasBase2 = Base2
+    type AliasIntf1 = Intf1
+    type AliasMix1 = Mix1
+
     var b1 = Base1.new()
     var b2 = Base2.new()
     var b3 = Base3.new()
@@ -3336,8 +3341,13 @@
     assert_true(instanceof(b2, Base1))
     assert_false(instanceof(b1, Base2))
     assert_true(instanceof(b3, Mix1))
-    assert_false(instanceof(b3, []))
-    assert_true(instanceof(b3, [Base1, Base2, Intf1]))
+    assert_true(instanceof(b3, Base1, Base2, Intf1))
+
+    assert_true(instanceof(b1, AliasBase1))
+    assert_true(instanceof(b2, AliasBase1))
+    assert_false(instanceof(b1, AliasBase2))
+    assert_true(instanceof(b3, AliasMix1))
+    assert_true(instanceof(b3, AliasBase1, AliasBase2, AliasIntf1))
 
     def Foo()
       var a1 = Base1.new()
@@ -3348,8 +3358,13 @@
       assert_true(instanceof(a2, Base1))
       assert_false(instanceof(a1, Base2))
       assert_true(instanceof(a3, Mix1))
-      assert_false(instanceof(a3, []))
-      assert_true(instanceof(a3, [Base1, Base2, Intf1]))
+      assert_true(instanceof(a3, Base1, Base2, Intf1))
+
+      assert_true(instanceof(a1, AliasBase1))
+      assert_true(instanceof(a2, AliasBase1))
+      assert_false(instanceof(a1, AliasBase2))
+      assert_true(instanceof(a3, AliasMix1))
+      assert_true(instanceof(a3, AliasBase1, AliasBase2, AliasIntf1))
     enddef
     Foo()
 
@@ -3358,6 +3373,58 @@
 
   END
   v9.CheckSourceSuccess(lines)
+
+  lines =<< trim END
+    vim9script
+
+    class Base1
+    endclass
+    instanceof(Base1.new())
+  END
+  v9.CheckSourceFailure(lines, 'E119: Not enough arguments for function: instanceof')
+
+  lines =<< trim END
+    vim9script
+
+    class Base1
+    endclass
+    def F()
+      instanceof(Base1.new())
+    enddef
+    F()
+  END
+  v9.CheckSourceFailure(lines, 'E119: Not enough arguments for function: instanceof')
+
+  lines =<< trim END
+    vim9script
+
+    class Base1
+    endclass
+
+    class Base2
+    endclass
+
+    var o = Base2.new()
+    instanceof(o, Base1, Base2, 3)
+  END
+  v9.CheckSourceFailure(lines, 'E693: Class or class typealias required for argument 4', 10)
+
+  lines =<< trim END
+    vim9script
+
+    class Base1
+    endclass
+
+    class Base2
+    endclass
+
+    def F()
+      var o = Base2.new()
+      instanceof(o, Base1, Base2, 3)
+    enddef
+    F()
+  END
+  v9.CheckSourceFailure(lines, 'E693: Class or class typealias required for argument 4')
 enddef
 
 " Test for calling a method in the parent class that is extended partially.
diff --git a/src/testdir/test_vim9_typealias.vim b/src/testdir/test_vim9_typealias.vim
index 34c9e0e..2082934 100644
--- a/src/testdir/test_vim9_typealias.vim
+++ b/src/testdir/test_vim9_typealias.vim
@@ -212,7 +212,7 @@
     enddef
     Foo()
   END
-  v9.CheckSourceFailure(lines, 'E1406: Cannot use a Typealias as a variable or value', 1)
+  v9.CheckSourceFailure(lines, 'E1407: Cannot use a Typealias as a variable or value', 1)
 
   # Using type alias in an expression (script level)
   lines =<< trim END
@@ -516,8 +516,18 @@
     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]))
+    assert_fails('instanceof(o, Ntype)', 'E693: Class or class typealias required for argument 2')
+    assert_fails('instanceof(o, Ctype, Ntype)', 'E693: Class or class typealias required for argument 3')
+
+    def F()
+      var x = instanceof(o, Ntype)
+    enddef
+    assert_fails('F()', 'E693: Class or class typealias required for argument 2')
+
+    def G(): bool
+      return instanceof(o, Ctype)
+    enddef
+    assert_equal(1, G())
   END
   v9.CheckScriptSuccess(lines)
 enddef