diff --git a/src/main/kotlin/com/marvinelsen/chinese/transliteration/Syllable.kt b/src/main/kotlin/com/marvinelsen/chinese/transliteration/Syllable.kt
index 4b99ba6..8a5df55 100644
--- a/src/main/kotlin/com/marvinelsen/chinese/transliteration/Syllable.kt
+++ b/src/main/kotlin/com/marvinelsen/chinese/transliteration/Syllable.kt
@@ -13,6 +13,9 @@ data class Syllable(
         private val zhuyinToPinyin = pinyinToZhuyin.entries.associate { it.value to it.key }
         private val zhuyinToneMarkRegex = """[ˊˇˋ˙]""".toRegex()
 
+        fun isValidPinyinWithToneNumberSyllable(pinyinSyllable: String) =
+            pinyinSyllable.last().isDigit() && pinyinSyllable.last().digitToInt() in 1..5 && pinyinSyllable.lowercase() in pinyinToZhuyin
+
         fun fromPinyinWithToneNumber(pinyinWithToneNumber: String): Syllable {
             val pinyinWithoutNumber = pinyinWithToneNumber.substring(0, pinyinWithToneNumber.lastIndex)
             val lastCharacter = pinyinWithToneNumber.last()
@@ -42,7 +45,7 @@ data class Syllable(
             return Syllable(
                 zhuyinToPinyin[zhuyinWithoutToneMark]!!,
                 Tone.fromZhuyinToneMarkOrNull(zhuyin.last()) ?: Tone.fromZhuyinToneMarkOrNull(zhuyin.first())
-                    ?: Tone.FIRST
+                ?: Tone.FIRST
             )
         }