diff --git a/jerry-core/ecma/operations/ecma-function-object.c b/jerry-core/ecma/operations/ecma-function-object.c
index 5df630845..63bc1218c 100644
--- a/jerry-core/ecma/operations/ecma-function-object.c
+++ b/jerry-core/ecma/operations/ecma-function-object.c
@@ -366,14 +366,9 @@ ecma_op_function_has_instance (ecma_object_t *func_obj_p, /**< Function object *
 
   ecma_value_t ret_value = ecma_make_simple_value (ECMA_SIMPLE_VALUE_EMPTY);
 
-  if (ecma_get_object_type (func_obj_p) == ECMA_OBJECT_TYPE_FUNCTION)
+  if (ecma_get_object_type (func_obj_p) == ECMA_OBJECT_TYPE_FUNCTION
+      || ecma_get_object_type (func_obj_p) == ECMA_OBJECT_TYPE_EXTERNAL_FUNCTION)
   {
-    if (ecma_get_object_is_builtin (func_obj_p)
-        && ecma_builtin_function_is_routine (func_obj_p))
-    {
-      return ecma_raise_type_error (ECMA_ERR_MSG ("Function parameter cannot be built-in a function."));
-    }
-
     if (!ecma_is_value_object (value))
     {
       return ecma_make_simple_value (ECMA_SIMPLE_VALUE_FALSE);
@@ -389,7 +384,7 @@ ecma_op_function_has_instance (ecma_object_t *func_obj_p, /**< Function object *
 
     if (!ecma_is_value_object (prototype_obj_value))
     {
-      ret_value = ecma_raise_type_error (ECMA_ERR_MSG ("Expected an object."));
+      ret_value = ecma_raise_type_error (ECMA_ERR_MSG ("Object expected."));
     }
     else
     {
@@ -419,10 +414,6 @@ ecma_op_function_has_instance (ecma_object_t *func_obj_p, /**< Function object *
 
     ecma_deref_ecma_string (prototype_magic_string_p);
   }
-  else if (ecma_get_object_type (func_obj_p) == ECMA_OBJECT_TYPE_EXTERNAL_FUNCTION)
-  {
-    ret_value = ecma_raise_type_error (ECMA_ERR_MSG ("Expected a function."));
-  }
   else
   {
     JERRY_ASSERT (ecma_get_object_type (func_obj_p) == ECMA_OBJECT_TYPE_BOUND_FUNCTION);
diff --git a/tests/jerry/function-external.js b/tests/jerry/function-external.js
new file mode 100644
index 000000000..d6eae3922
--- /dev/null
+++ b/tests/jerry/function-external.js
@@ -0,0 +1,43 @@
+// Copyright JS Foundation and other contributors, http://js.foundation
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+try {
+  ({} instanceof assert);
+  assert(false);
+} catch(e) {
+  assert(e instanceof TypeError);
+}
+
+assert.prototype = {}
+
+try {
+  assert(!({} instanceof assert));
+} catch(e) {
+  assert(false);
+}
+
+try {
+  ({} instanceof Math.sin);
+  assert(false);
+} catch(e) {
+  assert(e instanceof TypeError);
+}
+
+Math.sin.prototype = {}
+
+try {
+  assert(!({} instanceof Math.sin));
+} catch(e) {
+  assert(false);
+}
diff --git a/tests/jerry/regression-test-issue-736.js b/tests/jerry/regression-test-issue-736.js
index 8a1403e39..9d31f7365 100644
--- a/tests/jerry/regression-test-issue-736.js
+++ b/tests/jerry/regression-test-issue-736.js
@@ -31,7 +31,7 @@ try {
 }
 
 try {
-  eval("var x; x instanceof assert;");
+  eval("var x = {}; x instanceof assert;");
   assert(false);
 } catch(e) {
   assert(e instanceof TypeError);