diff --git a/crates/voicevox_core/src/synthesizer.rs b/crates/voicevox_core/src/synthesizer.rs
index 2e97fbe1c..73b4a6696 100644
--- a/crates/voicevox_core/src/synthesizer.rs
+++ b/crates/voicevox_core/src/synthesizer.rs
@@ -141,6 +141,9 @@ mod inner {
                 frame_length = audio.frame_length,
             );
         }
+        if range.start > range.end {
+            panic!("{range:?} is invalid because start > end",);
+        }
         let range = range.start..range.end + 2 * MARGIN;
         audio.internal_state.slice(ndarray::s![range, ..])
     }
diff --git a/crates/voicevox_core_python_api/src/lib.rs b/crates/voicevox_core_python_api/src/lib.rs
index 3f3a51cb1..25eb2b33f 100644
--- a/crates/voicevox_core_python_api/src/lib.rs
+++ b/crates/voicevox_core_python_api/src/lib.rs
@@ -718,6 +718,12 @@ mod blocking {
                     audio.frame_length(),
                 )));
             }
+            if start > end {
+                return Err(PyIndexError::new_err(format!(
+                    "({}, {}) is invalid range because start > end",
+                    start, end,
+                )));
+            }
             let wav = &self
                 .synthesizer
                 .read()?