diff --git a/build.gradle.kts b/build.gradle.kts
index af2c3e7..2dc74ee 100644
--- a/build.gradle.kts
+++ b/build.gradle.kts
@@ -5,7 +5,7 @@ plugins {
 }
 
 group = "com.marvinelsen"
-version = "1.0-SNAPSHOT"
+version = "1.1-SNAPSHOT"
 
 repositories {
     mavenCentral()
diff --git a/src/main/kotlin/com/marvinelsen/chinese/transliteration/Syllable.kt b/src/main/kotlin/com/marvinelsen/chinese/transliteration/Syllable.kt
index ce31655..bea85f1 100644
--- a/src/main/kotlin/com/marvinelsen/chinese/transliteration/Syllable.kt
+++ b/src/main/kotlin/com/marvinelsen/chinese/transliteration/Syllable.kt
@@ -15,7 +15,9 @@ data class Syllable(
         private val zhuyinToneMarkRegex = """[ˊˇˋ˙]""".toRegex()
 
         fun isValidPinyinWithToneNumberSyllable(pinyinSyllable: String) =
-            pinyinSyllable.last().isDigit() && pinyinSyllable.last().digitToInt() in 1..5 && pinyinSyllable.lowercase() in pinyinToZhuyin
+            pinyinSyllable.last().isDigit() && pinyinSyllable.last().digitToInt() in 1..5 && pinyinSyllable
+                .substring(0, pinyinSyllable.lastIndex)
+                .lowercase() in pinyinToZhuyin
 
         fun fromPinyinWithToneNumber(pinyinWithToneNumber: String): Syllable {
             val pinyinWithoutNumber = pinyinWithToneNumber.substring(0, pinyinWithToneNumber.lastIndex)