diff --git a/jerry-core/ecma/base/ecma-helpers-string.c b/jerry-core/ecma/base/ecma-helpers-string.c
index 6b7cf2db0..410f8b158 100644
--- a/jerry-core/ecma/base/ecma-helpers-string.c
+++ b/jerry-core/ecma/base/ecma-helpers-string.c
@@ -273,7 +273,7 @@ ecma_new_ecma_string_from_utf8_converted_to_cesu8 (const lit_utf8_byte_t *string
 
     lit_utf8_byte_t *data_p;
 
-    if (likely (string_size <= UINT16_MAX))
+    if (likely (converted_string_size <= UINT16_MAX))
     {
       string_desc_p = ecma_alloc_string_buffer (sizeof (ecma_string_t) + converted_string_size);
 
diff --git a/tests/unit-core/test-strings.c b/tests/unit-core/test-strings.c
index 31218bdeb..a3b8b6b03 100644
--- a/tests/unit-core/test-strings.c
+++ b/tests/unit-core/test-strings.c
@@ -26,7 +26,7 @@
 #define test_subiters (128)
 
 /* Max bytes in string. */
-#define max_bytes_in_string (16 * 1024)
+#define max_bytes_in_string (65 * 1024)
 #define max_code_units_in_string (max_bytes_in_string)
 
 typedef enum