diff --git a/jerry-core/ecma/base/ecma-helpers-string.c b/jerry-core/ecma/base/ecma-helpers-string.c
index 2d859c0db..261bb1ac0 100644
--- a/jerry-core/ecma/base/ecma-helpers-string.c
+++ b/jerry-core/ecma/base/ecma-helpers-string.c
@@ -554,7 +554,7 @@ ecma_concat_ecma_strings (ecma_string_t *string1_p, /**< first ecma-string */
 
       utf8_string1_p = lit_get_magic_string_ex_utf8 (string1_p->u.magic_string_id);
       utf8_string1_size = lit_get_magic_string_ex_size (string1_p->u.magic_string_id);
-      utf8_string1_length = utf8_string1_size;
+      utf8_string1_length = lit_utf8_string_length (utf8_string1_p, utf8_string1_size);
       string1_rehash_needed = true;
       break;
     }
@@ -600,7 +600,7 @@ ecma_concat_ecma_strings (ecma_string_t *string1_p, /**< first ecma-string */
 
       utf8_string2_p = lit_get_magic_string_ex_utf8 (string2_p->u.magic_string_id);
       utf8_string2_size = lit_get_magic_string_ex_size (string2_p->u.magic_string_id);
-      utf8_string2_length = utf8_string2_size;
+      utf8_string2_length = lit_utf8_string_length (utf8_string2_p, utf8_string2_size);
       break;
     }
   }
@@ -1035,12 +1035,10 @@ ecma_string_raw_chars (const ecma_string_t *string_p, /**< ecma-string */
       JERRY_ASSERT (ECMA_STRING_GET_CONTAINER (string_p) == ECMA_STRING_CONTAINER_MAGIC_STRING_EX);
 
       size = lit_get_magic_string_ex_size (string_p->u.magic_string_ex_id);
-      length = size;
+      length = lit_utf8_string_length (lit_get_magic_string_ex_utf8 (string_p->u.magic_string_ex_id),
+                                       lit_get_magic_string_ex_size (string_p->u.magic_string_ex_id));
 
       result_p = lit_get_magic_string_ex_utf8 (string_p->u.magic_string_ex_id);
-
-      /* All extended magic strings must be ascii strings. */
-      JERRY_ASSERT (ECMA_STRING_IS_ASCII (result_p, size));
       break;
     }
   }
@@ -1472,9 +1470,8 @@ ecma_string_get_length (const ecma_string_t *string_p) /**< ecma-string */
     {
       JERRY_ASSERT (ECMA_STRING_GET_CONTAINER (string_p) == ECMA_STRING_CONTAINER_MAGIC_STRING_EX);
 
-      JERRY_ASSERT (ECMA_STRING_IS_ASCII (lit_get_magic_string_ex_utf8 (string_p->u.magic_string_ex_id),
-                                          lit_get_magic_string_ex_size (string_p->u.magic_string_ex_id)));
-      return lit_get_magic_string_ex_size (string_p->u.magic_string_ex_id);
+      return lit_utf8_string_length (lit_get_magic_string_ex_utf8 (string_p->u.magic_string_ex_id),
+                                     lit_get_magic_string_ex_size (string_p->u.magic_string_ex_id));
     }
   }
 } /* ecma_string_get_length */
diff --git a/tests/unit/test-api.c b/tests/unit/test-api.c
index 6e74be0ab..82590a83d 100644
--- a/tests/unit/test-api.c
+++ b/tests/unit/test-api.c
@@ -151,8 +151,8 @@ handler_construct (const jerry_value_t func_obj_val, /**< function object */
  */
 #define JERRY_MAGIC_STRING_ITEMS \
   JERRY_MAGIC_STRING_DEF (GLOBAL, global) \
-  JERRY_MAGIC_STRING_DEF (CONSOLE, console)
-
+  JERRY_MAGIC_STRING_DEF (CONSOLE, console) \
+  JERRY_MAGIC_STRING_DEF (GREEK_ZERO_SIGN, \xed\xa0\x80\xed\xb6\x8a)
 
 #define JERRY_MAGIC_STRING_DEF(NAME, STRING) \
   static const char jerry_magic_string_ex_ ## NAME[] = # STRING;
@@ -832,6 +832,34 @@ main (void)
   jerry_release_value (res);
   jerry_release_value (parsed_code_val);
 
+  /* call jerry_create_string functions which will returns with the registered external magic strings */
+  args[0] = jerry_create_string ((jerry_char_t *) "console");
+  args[1] = jerry_create_string ((jerry_char_t *) "\xed\xa0\x80\xed\xb6\x8a"); /**< greek zero sign */
+
+  cesu8_length = jerry_get_string_length (args[0]);
+  cesu8_sz = jerry_get_string_size (args[0]);
+
+  char string_console[cesu8_sz];
+  jerry_string_to_char_buffer (args[0], (jerry_char_t *) string_console, cesu8_sz);
+
+  TEST_ASSERT (!strncmp (string_console, "console", cesu8_sz));
+  TEST_ASSERT (cesu8_length == 7);
+  TEST_ASSERT (cesu8_length == cesu8_sz);
+
+  jerry_release_value (args[0]);
+
+  cesu8_length = jerry_get_string_length (args[1]);
+  cesu8_sz = jerry_get_string_size (args[1]);
+
+  char string_greek_zero_sign[cesu8_sz];
+  jerry_string_to_char_buffer (args[1], (jerry_char_t *) string_greek_zero_sign, cesu8_sz);
+
+  TEST_ASSERT (!strncmp (string_greek_zero_sign, "\xed\xa0\x80\xed\xb6\x8a", cesu8_sz));
+  TEST_ASSERT (cesu8_length == 2);
+  TEST_ASSERT (cesu8_sz == 6);
+
+  jerry_release_value (args[1]);
+
   jerry_cleanup ();
 
   /* Dump / execute snapshot */