diff --git a/evaluate_expression.go b/evaluate_expression.go
index 52274df..7e5a00c 100644
--- a/evaluate_expression.go
+++ b/evaluate_expression.go
@@ -250,7 +250,7 @@ func (self *_runtime) calculateBinaryOperation(operator string, left Value, righ
 	case "instanceof":
 		rightValue := self.GetValue(right)
 		if !rightValue.IsObject() {
-			panic(newTypeError())
+			panic(newTypeError("Expecting a function in instanceof check, but got: %v", rightValue))
 		}
 		return toValue(rightValue._object().HasInstance(leftValue))
 
diff --git a/otto_test.go b/otto_test.go
index 704c0ad..1c6c055 100644
--- a/otto_test.go
+++ b/otto_test.go
@@ -1159,15 +1159,24 @@ func TestParenthesizing(t *testing.T) {
 	test("jkl", "true")
 }
 
-func TestInstanceOf(t *testing.T) {
+func Test_instanceof(t *testing.T) {
 	Terst(t)
 
 	test := runTest()
 
 	test(`
-		abc = {} instanceof Object
+		abc = {} instanceof Object;
 	`)
 	test("abc", "true")
+
+	test(`
+		abc = "abc" instanceof Object;
+	`)
+	test("abc", "false")
+
+	test(`raise:
+		abc = {} instanceof "abc";
+    `, "TypeError: Expecting a function in instanceof check, but got: abc")
 }
 
 func TestIn(t *testing.T) {
diff --git a/type_function.go b/type_function.go
index 9f404a0..b2845b3 100644
--- a/type_function.go
+++ b/type_function.go
@@ -69,7 +69,7 @@ func (self *_object) CallSet(name string, value Value) {
 // 15.3.5.3
 func (self *_object) HasInstance(of Value) bool {
 	if !of.IsObject() {
-		panic(newTypeError())
+		return false
 	}
 	prototype := self.get("prototype")
 	if !prototype.IsObject() {