diff --git a/src/libecmaobjects/ecma-globals.h b/src/libecmaobjects/ecma-globals.h
index 7f96c622c..5df5b7d3e 100644
--- a/src/libecmaobjects/ecma-globals.h
+++ b/src/libecmaobjects/ecma-globals.h
@@ -466,7 +466,7 @@ typedef float ecma_number_t;
 /**
  * Maximum number of characters in string representation of ecma-number
  */
-#define ECMA_MAX_CHARS_IN_STRINGIFIED_NUMBER 512
+#define ECMA_MAX_CHARS_IN_STRINGIFIED_NUMBER 64
 
 /**
  * Maximum number of characters in string representation of ecma-uint32
diff --git a/src/libecmaobjects/ecma-helpers-conversion.c b/src/libecmaobjects/ecma-helpers-conversion.c
index a90c5c5a9..f403c3792 100644
--- a/src/libecmaobjects/ecma-helpers-conversion.c
+++ b/src/libecmaobjects/ecma-helpers-conversion.c
@@ -134,11 +134,13 @@ ecma_number_to_int32 (ecma_number_t value) /**< unsigned 32-bit integer value */
  *
  * See also:
  *          ECMA-262 v5, 9.8.1
+ *
+ * @return length of zt-string
  */
-void
+ecma_length_t
 ecma_number_to_zt_string (ecma_number_t num, /**< ecma-number */
                           ecma_char_t *buffer_p, /**< buffer for zt-string */
-                          size_t buffer_size) /**< size of buffer */
+                          ssize_t buffer_size) /**< size of buffer */
 {
   TODO (Support UTF-16);
 
@@ -149,161 +151,159 @@ ecma_number_to_zt_string (ecma_number_t num, /**< ecma-number */
   ecma_char_t e_char = 'e';
   ecma_char_t null_char = '\0';
 
-  // 1.
   if (ecma_number_is_nan (num))
   {
+    // 1.
     FIXME (/* Assert that buffer's size is enough */);
-    __strncpy ((char*) buffer_p, (char*) ecma_get_magic_string_zt (ECMA_MAGIC_STRING_NAN), buffer_size);
-
-    return;
-  }
-
-  ecma_char_t *dst_p = buffer_p;
-
-  // 2.
-  if (ecma_number_is_zero (num))
-  {
-    *dst_p++ = digits_chars[0];
-    *dst_p++ = null_char;
-
-    JERRY_ASSERT ((uint8_t*)dst_p - (uint8_t*)buffer_p <= (ssize_t) buffer_size);
-
-    return;
-  }
-
-  // 3.
-  if (ecma_number_is_negative (num))
-  {
-    *dst_p++ = minus_char;
-    size_t new_buffer_size = (size_t) ((ssize_t) buffer_size - ((uint8_t*)dst_p - (uint8_t*)buffer_p));
-    ecma_number_to_zt_string (ecma_number_negate (num), dst_p, new_buffer_size);
-
-    return;
-  }
-
-  // 4.
-  if (ecma_number_is_infinity (num))
-  {
-    FIXME (/* Assert that buffer's size is enough */);
-    __strncpy ((char*) buffer_p, (char*) ecma_get_magic_string_zt (ECMA_MAGIC_STRING_INFINITY), buffer_size);
-
-    return;
-  }
-
-  // 5.
-  uint64_t fraction;
-  int32_t exponent;
-  int32_t dot_shift;
-  dot_shift = ecma_number_get_fraction_and_exponent (num, &fraction, &exponent);
-
-  FIXME (Decimal representation);
-
-  uint64_t s = fraction;
-  int32_t n = exponent + 1;
-  int32_t k = dot_shift;
-
-  JERRY_ASSERT (s != 0);
-  while (!(s & 1))
-  {
-    s >>= 1;
-    k--;
-  }
-
-  // 6.
-  if (k <= n && n <= 21)
-  {
-    for (int32_t i = 0; i < k; i++)
-    {
-      uint64_t bit_mask = 1ul << (k - i - 1);
-      *dst_p++ = digits_chars [(s & bit_mask) ? 1 : 0];
-    }
-
-    for (int32_t i = 0; i < n - k; i++)
-    {
-      *dst_p++ = digits_chars[0];
-    }
-  }
-  else if (0 < n && n <= 21)
-  {
-    // 7.
-    for (int32_t i = 0; i < n; i++)
-    {
-      uint64_t bit_mask = 1ul << (k - i - 1);
-      *dst_p++ = digits_chars [(s & bit_mask) ? 1 : 0];
-    }
-
-    *dst_p++ = dot_char;
-
-    for (int32_t i = n; i < k; i++)
-    {
-      uint64_t bit_mask = 1ul << (k - i - 1);
-      *dst_p++ = digits_chars [(s & bit_mask) ? 1 : 0];
-    }
-  }
-  else if (-6 <= n && n <= 0)
-  {
-    // 8.
-    *dst_p++ = digits_chars[0];
-    *dst_p++ = '.';
-
-    for (int32_t i = 0; i < k; i++)
-    {
-      uint64_t bit_mask = 1ul << (k - i - 1);
-      *dst_p++ = digits_chars [(s & bit_mask) ? 1 : 0];
-    }
+    __strncpy ((char*) buffer_p, (char*) ecma_get_magic_string_zt (ECMA_MAGIC_STRING_NAN), (size_t) buffer_size);
   }
   else
   {
-    if (k == 1)
-    {
-      // 9.
-      *dst_p++ = digits_chars [s ? 1 : 0];
-    }
-    else
-    {
-      // 10.
-      uint64_t bit_mask = 1ul << (k - 1);
-      *dst_p++ = digits_chars [(s & bit_mask) ? 1 : 0];
-      *dst_p++ = dot_char;
-      for (int32_t i = 1; i < k; i++)
-      {
-        bit_mask = 1ul << (k - i - 1);
-        *dst_p++ = digits_chars [(s & bit_mask) ? 1 : 0];
-      }
-    }
+    ecma_char_t *dst_p = buffer_p;
 
-    // 9., 10.
-    *dst_p++ = e_char;
-    *dst_p++ = (n >= 1) ? plus_char : minus_char;
-    int32_t t = (n >= 1) ? (n - 1) : -(n - 1);
-
-    if (t == 0)
+    if (ecma_number_is_zero (num))
     {
+      // 2.
       *dst_p++ = digits_chars[0];
+      *dst_p++ = null_char;
+
+      JERRY_ASSERT ((uint8_t*)dst_p - (uint8_t*)buffer_p <= (ssize_t) buffer_size);
+    }
+    else if (ecma_number_is_negative (num))
+    {
+      // 3.
+      *dst_p++ = minus_char;
+      ssize_t new_buffer_size = (buffer_size - ((uint8_t*)dst_p - (uint8_t*)buffer_p));
+      ecma_number_to_zt_string (ecma_number_negate (num), dst_p, new_buffer_size);
+    }
+    else if (ecma_number_is_infinity (num))
+    {
+      // 4.
+      FIXME (/* Assert that buffer's size is enough */);
+      __strncpy ((char*) buffer_p, (char*) ecma_get_magic_string_zt (ECMA_MAGIC_STRING_INFINITY), (size_t) buffer_size);
     }
     else
     {
-      uint32_t t_bit = (1u << 31);
+      // 5.
+      uint64_t fraction;
+      int32_t exponent;
+      int32_t dot_shift;
+      dot_shift = ecma_number_get_fraction_and_exponent (num, &fraction, &exponent);
 
-      while ((t & (int32_t) t_bit) == 0)
+      FIXME (Decimal representation);
+
+      uint64_t s = fraction;
+      int32_t n = exponent + 1;
+      int32_t k = dot_shift;
+
+      JERRY_ASSERT (s != 0);
+      while (!(s & 1))
       {
-        t_bit >>= 1;
-
-        JERRY_ASSERT (t_bit != 0);
+        s >>= 1;
+        k--;
       }
 
-      while (t_bit != 0)
+      // 6.
+      if (k <= n && n <= 21)
       {
-        *dst_p++ = digits_chars [(t & (int32_t) t_bit) ? 1 : 0];
+        for (int32_t i = 0; i < k; i++)
+        {
+          uint64_t bit_mask = 1ul << (k - i - 1);
+          *dst_p++ = digits_chars [(s & bit_mask) ? 1 : 0];
+        }
 
-        t_bit >>= 1;
+        for (int32_t i = 0; i < n - k; i++)
+        {
+          *dst_p++ = digits_chars[0];
+        }
       }
+      else if (0 < n && n <= 21)
+      {
+        // 7.
+        for (int32_t i = 0; i < n; i++)
+        {
+          uint64_t bit_mask = 1ul << (k - i - 1);
+          *dst_p++ = digits_chars [(s & bit_mask) ? 1 : 0];
+        }
+
+        *dst_p++ = dot_char;
+
+        for (int32_t i = n; i < k; i++)
+        {
+          uint64_t bit_mask = 1ul << (k - i - 1);
+          *dst_p++ = digits_chars [(s & bit_mask) ? 1 : 0];
+        }
+      }
+      else if (-6 <= n && n <= 0)
+      {
+        // 8.
+        *dst_p++ = digits_chars[0];
+        *dst_p++ = '.';
+
+        for (int32_t i = 0; i < k; i++)
+        {
+          uint64_t bit_mask = 1ul << (k - i - 1);
+          *dst_p++ = digits_chars [(s & bit_mask) ? 1 : 0];
+        }
+      }
+      else
+      {
+        if (k == 1)
+        {
+          // 9.
+          *dst_p++ = digits_chars [s ? 1 : 0];
+        }
+        else
+        {
+          // 10.
+          uint64_t bit_mask = 1ul << (k - 1);
+          *dst_p++ = digits_chars [(s & bit_mask) ? 1 : 0];
+          *dst_p++ = dot_char;
+          for (int32_t i = 1; i < k; i++)
+          {
+            bit_mask = 1ul << (k - i - 1);
+            *dst_p++ = digits_chars [(s & bit_mask) ? 1 : 0];
+          }
+        }
+
+        // 9., 10.
+        *dst_p++ = e_char;
+        *dst_p++ = (n >= 1) ? plus_char : minus_char;
+        int32_t t = (n >= 1) ? (n - 1) : -(n - 1);
+
+        if (t == 0)
+        {
+          *dst_p++ = digits_chars[0];
+        }
+        else
+        {
+          uint32_t t_bit = (1u << 31);
+
+          while ((t & (int32_t) t_bit) == 0)
+          {
+            t_bit >>= 1;
+
+            JERRY_ASSERT (t_bit != 0);
+          }
+
+          while (t_bit != 0)
+          {
+            *dst_p++ = digits_chars [(t & (int32_t) t_bit) ? 1 : 0];
+
+            t_bit >>= 1;
+          }
+        }
+      }
+
+      *dst_p++ = null_char;
+
+      JERRY_ASSERT ((uint8_t*)dst_p - (uint8_t*)buffer_p <= (ssize_t) buffer_size);
     }
   }
 
-  *dst_p++ = null_char;
+  ecma_length_t length = (ecma_length_t) __strlen ((char*) buffer_p);
 
-  JERRY_ASSERT ((uint8_t*)dst_p - (uint8_t*)buffer_p <= (ssize_t) buffer_size);
+  return length;
 } /* ecma_number_to_zt_string */
 
 /**
diff --git a/src/libecmaobjects/ecma-helpers-string.c b/src/libecmaobjects/ecma-helpers-string.c
index 9414cc844..b370cc96f 100644
--- a/src/libecmaobjects/ecma-helpers-string.c
+++ b/src/libecmaobjects/ecma-helpers-string.c
@@ -246,7 +246,7 @@ ecma_get_ecma_string_length (ecma_string_t *string_desc_p) /**< ecma-string desc
  * Convert ecma-string to number
  */
 ecma_number_t
-ecma_string_to_number (const ecma_string_t *str_p) /**< ecma-string */
+ecma_string_to_number (ecma_string_t *str_p) /**< ecma-string */
 {
   JERRY_ASSERT (str_p != NULL);
 
@@ -264,13 +264,46 @@ ecma_string_to_number (const ecma_string_t *str_p) /**< ecma-string */
 
     ssize_t bytes_copied = ecma_string_to_zt_string (str_p,
                                                      zt_string_buffer,
-                                                     sizeof (zt_string_buffer));
+                                                     (ssize_t) sizeof (zt_string_buffer));
     JERRY_ASSERT (bytes_copied > 0);
-    
+
     return ecma_zt_string_to_number (zt_string_buffer);
   }
 } /* ecma_string_to_number */
 
+/**
+ * Get size of buffer required to store the ecma-string in zt-form.
+ */
+static ssize_t
+ecma_string_get_required_buffer_size_for_zt_form (const ecma_string_t *string_desc_p) /**< ecma-string */
+{
+  ecma_length_t string_length = 0;
+
+  switch ((ecma_string_container_t)string_desc_p->container)
+  {
+    case ECMA_STRING_CONTAINER_IN_DESCRIPTOR:
+    case ECMA_STRING_CONTAINER_HEAP_CHUNKS:
+    case ECMA_STRING_CONTAINER_LIT_TABLE:
+    {
+      JERRY_ASSERT (string_desc_p->is_length_valid);
+
+      string_length = string_desc_p->length;
+
+      break;
+    }
+
+    case ECMA_STRING_CONTAINER_HEAP_NUMBER:
+    {
+      string_length = (string_desc_p->is_length_valid ?
+                       string_desc_p->length : ECMA_MAX_CHARS_IN_STRINGIFIED_NUMBER);
+
+      break;
+    }
+  }
+
+  return (ssize_t) ((ssize_t) sizeof (ecma_char_t) * (string_length + 1));
+} /* ecma_string_get_required_buffer_size_for_zt_form */
+
 /**
  * Copy ecma-string's contents to a buffer.
  *
@@ -281,23 +314,21 @@ ecma_string_to_number (const ecma_string_t *str_p) /**< ecma-string */
  *         as negation of buffer size, that is required to hold the string's content.
  */
 ssize_t
-ecma_string_to_zt_string (const ecma_string_t *string_desc_p, /**< ecma-string descriptor */
+ecma_string_to_zt_string (ecma_string_t *string_desc_p, /**< ecma-string descriptor */
                           ecma_char_t *buffer_p, /**< destination buffer */
-                          size_t buffer_size) /**< size of buffer */
+                          ssize_t buffer_size) /**< size of buffer */
 {
   JERRY_ASSERT (string_desc_p != NULL);
   JERRY_ASSERT (string_desc_p->refs > 0);
   JERRY_ASSERT (buffer_p != NULL);
   JERRY_ASSERT (buffer_size > 0);
 
-  JERRY_ASSERT (string_desc_p->is_length_valid);
-
-  const ecma_length_t string_length = string_desc_p->length;
-  size_t required_buffer_size = sizeof (ecma_char_t) * string_length + 1 /* for zero char */;
+  ssize_t required_buffer_size = ecma_string_get_required_buffer_size_for_zt_form (string_desc_p);
+  ssize_t bytes_copied = 0;
 
   if (required_buffer_size > buffer_size)
   {
-    return - (ssize_t) required_buffer_size;
+    return -required_buffer_size;
   }
 
   ecma_char_t *dest_p = buffer_p;
@@ -306,13 +337,21 @@ ecma_string_to_zt_string (const ecma_string_t *string_desc_p, /**< ecma-string d
   {
     case ECMA_STRING_CONTAINER_IN_DESCRIPTOR:
     {
+      JERRY_ASSERT (string_desc_p->is_length_valid);
+      ecma_length_t string_length = string_desc_p->length;
+
       __memcpy (dest_p, string_desc_p->u.chars, string_length * sizeof (ecma_char_t));
       dest_p += string_length;
+      *dest_p++ = '\0';
+      bytes_copied = (dest_p - buffer_p) * ((ssize_t) sizeof (ecma_char_t));
 
       break;
     }
     case ECMA_STRING_CONTAINER_HEAP_CHUNKS:
     {
+      JERRY_ASSERT (string_desc_p->is_length_valid);
+      ecma_length_t string_length = string_desc_p->length;
+
       ecma_collection_chunk_t *string_chunk_p = ECMA_GET_POINTER (string_desc_p->u.chunk_cp);
 
       const ecma_length_t max_chars_in_chunk = sizeof (string_chunk_p->data) / sizeof (ecma_char_t);
@@ -330,18 +369,47 @@ ecma_string_to_zt_string (const ecma_string_t *string_desc_p, /**< ecma-string d
 
         string_chunk_p = ECMA_GET_POINTER(string_chunk_p->next_chunk_cp);
       }
+      *dest_p++ = '\0';
+      bytes_copied = (dest_p - buffer_p) * ((ssize_t) sizeof (ecma_char_t));
+
       break;
     }
     case ECMA_STRING_CONTAINER_LIT_TABLE:
+    {
+      bytes_copied = try_get_string_by_idx ((uint8_t) string_desc_p->u.lit_index,
+                                            buffer_p,
+                                            buffer_size);
+
+      break;
+    }
     case ECMA_STRING_CONTAINER_HEAP_NUMBER:
     {
-      JERRY_UNIMPLEMENTED();
+      const ssize_t buffer_size_required = (ECMA_MAX_CHARS_IN_STRINGIFIED_NUMBER + 1) * sizeof (ecma_char_t);
+      if (buffer_size_required < buffer_size)
+      {
+        return -(ssize_t) buffer_size_required;
+      }
+
+      ecma_number_t *num_p = ECMA_GET_POINTER (string_desc_p->u.number_cp);
+
+      ecma_length_t length = ecma_number_to_zt_string (*num_p, buffer_p, buffer_size);
+
+      if (!string_desc_p->is_length_valid)
+      {
+        string_desc_p->length = length;
+        string_desc_p->is_length_valid = true;
+      }
+
+      JERRY_ASSERT (string_desc_p->is_length_valid
+                    && string_desc_p->length == length);
+
+      bytes_copied = (length + 1) * ((ssize_t) sizeof (ecma_char_t));
     }
   }
 
-  *dest_p = '\0';
+  JERRY_ASSERT (bytes_copied > 0 && bytes_copied <= required_buffer_size);
 
-  return (ssize_t) required_buffer_size;
+  return bytes_copied;
 } /* ecma_string_to_zt_string */
 
 /**
diff --git a/src/libecmaobjects/ecma-helpers.h b/src/libecmaobjects/ecma-helpers.h
index e2c21e413..d9979f4db 100644
--- a/src/libecmaobjects/ecma-helpers.h
+++ b/src/libecmaobjects/ecma-helpers.h
@@ -92,10 +92,10 @@ extern ecma_string_t* ecma_new_ecma_string_from_lit_index (literal_index_t lit_i
 extern void ecma_ref_ecma_string (ecma_string_t *string_desc_p);
 extern void ecma_deref_ecma_string (ecma_string_t *string_p);
 extern ecma_length_t ecma_get_ecma_string_length (ecma_string_t *string_desc_p);
-extern ecma_number_t ecma_string_to_number (const ecma_string_t *str_p);
-extern ssize_t ecma_string_to_zt_string (const ecma_string_t *string_desc_p,
+extern ecma_number_t ecma_string_to_number (ecma_string_t *str_p);
+extern ssize_t ecma_string_to_zt_string (ecma_string_t *string_desc_p,
                                          ecma_char_t *buffer_p,
-                                         size_t buffer_size);
+                                         ssize_t buffer_size);
 extern int32_t ecma_compare_zt_string_to_zt_string (const ecma_char_t *string1_p, const ecma_char_t *string2_p);
 extern bool ecma_compare_ecma_string_to_ecma_string (const ecma_string_t *string1_p,
                                                      const ecma_string_t *string2_p);
@@ -190,7 +190,7 @@ extern void ecma_uint32_to_string (uint32_t value, ecma_char_t *out_buffer_p, si
 extern uint32_t ecma_number_to_uint32 (ecma_number_t value);
 extern int32_t ecma_number_to_int32 (ecma_number_t value);
 extern ecma_number_t ecma_uint32_to_number (uint32_t value);
-extern void ecma_number_to_zt_string (ecma_number_t num, ecma_char_t *buffer_p, size_t buffer_size);
+extern ecma_length_t ecma_number_to_zt_string (ecma_number_t num, ecma_char_t *buffer_p, ssize_t buffer_size);
 
 #endif /* !JERRY_ECMA_HELPERS_H */