diff --git a/crates/voicevox_core/src/engine/acoustic_feature_extractor.rs b/crates/voicevox_core/src/engine/acoustic_feature_extractor.rs
index 87b634e11..8dac7c06a 100644
--- a/crates/voicevox_core/src/engine/acoustic_feature_extractor.rs
+++ b/crates/voicevox_core/src/engine/acoustic_feature_extractor.rs
@@ -63,10 +63,6 @@ static PHONEME_MAP: LazyLock<HashMap<&str, i64>> = LazyLock::new(|| {
 #[derive(Debug, Clone, PartialEq, new, Default, Getters)]
 pub(crate) struct OjtPhoneme {
     phoneme: String,
-    // FIXME: derive-getters(多分)が警告を覆い隠しているが、以下の二つは使っていないはず。`Debug`用
-    // に持つというのはありかもしれないが…
-    start: f32,
-    end: f32,
 }
 
 impl OjtPhoneme {
@@ -114,8 +110,8 @@ mod tests {
     fn base_hello_hiho() -> Vec<OjtPhoneme> {
         STR_HELLO_HIHO
             .split_whitespace()
-            .enumerate()
-            .map(|(i, s)| OjtPhoneme::new(s.into(), i as f32, (i + 1) as f32))
+            .map(ToOwned::to_owned)
+            .map(OjtPhoneme::new)
             .collect()
     }
 
@@ -155,9 +151,9 @@ mod tests {
     }
 
     #[rstest]
-    #[case(ojt_hello_hiho(), 9, OjtPhoneme::new("a".into(), 9., 10.), true)]
-    #[case(ojt_hello_hiho(), 9, OjtPhoneme::new("k".into(), 9., 10.), false)]
-    #[case(ojt_hello_hiho(), 9, OjtPhoneme::new("a".into(), 10., 11.), false)]
+    #[case(ojt_hello_hiho(), 9, OjtPhoneme::new("a".into()), true)]
+    #[case(ojt_hello_hiho(), 9, OjtPhoneme::new("k".into()), false)]
+    #[case(ojt_hello_hiho(), 9, OjtPhoneme::new("a".into()), false)]
     fn test_ojt_phoneme_equality(
         #[case] ojt_phonemes: Vec<OjtPhoneme>,
         #[case] index: usize,
diff --git a/crates/voicevox_core/src/synthesizer.rs b/crates/voicevox_core/src/synthesizer.rs
index 045a2d9ea..ee960cd1a 100644
--- a/crates/voicevox_core/src/synthesizer.rs
+++ b/crates/voicevox_core/src/synthesizer.rs
@@ -1079,8 +1079,9 @@ pub(crate) mod blocking {
             OjtPhoneme::convert(
                 phoneme_str_list
                     .iter()
-                    .enumerate()
-                    .map(|(i, s)| OjtPhoneme::new(s.as_ref().to_string(), i as f32, i as f32 + 1.))
+                    .map(AsRef::as_ref)
+                    .map(ToOwned::to_owned)
+                    .map(OjtPhoneme::new)
                     .collect::<Vec<OjtPhoneme>>()
                     .as_slice(),
             )