diff --git a/jerry-core/ecma/builtin-objects/ecma-builtin-number-prototype.cpp b/jerry-core/ecma/builtin-objects/ecma-builtin-number-prototype.cpp
index 5a0730244e..03763b0d43 100644
--- a/jerry-core/ecma/builtin-objects/ecma-builtin-number-prototype.cpp
+++ b/jerry-core/ecma/builtin-objects/ecma-builtin-number-prototype.cpp
@@ -97,7 +97,8 @@ ecma_builtin_number_prototype_object_to_string (ecma_value_t this_arg, /**< this
   if (arguments_list_len == 0
       || ecma_number_is_nan (this_arg_number)
       || ecma_number_is_infinity (this_arg_number)
-      || ecma_number_is_zero (this_arg_number))
+      || ecma_number_is_zero (this_arg_number)
+      || (arguments_list_len > 0 && ecma_is_value_undefined (arguments_list_p[0])))
   {
     ecma_string_t *ret_str_p = ecma_new_ecma_string_from_number (this_arg_number);
 
diff --git a/tests/jerry/number-prototype-to-string.js b/tests/jerry/number-prototype-to-string.js
index a1e669b398..64fef3bfee 100644
--- a/tests/jerry/number-prototype-to-string.js
+++ b/tests/jerry/number-prototype-to-string.js
@@ -43,6 +43,7 @@ assert((-0.0001).toString(4) === "-0.000000122031232023223013010030231")
 assert((-0).toString(16) === "0");
 assert((1e+73).toString(35) === "2nx1mg1l0w4ujlpt449c5qfrkkmtpgpsfsc2prlaqtnjbli2")
 assert((-1e+73).toString(35) === "-2nx1mg1l0w4ujlpt449c5qfrkkmtpgpsfsc2prlaqtnjbli2")
+assert((1).toString(undefined) === "1")
 
 assert((123400).toString(2) === "11110001000001000");
 assert((123400).toString(3) === "20021021101");