diff --git a/src/companion.rs b/src/companion.rs
index 8f0128e..785a8a2 100644
--- a/src/companion.rs
+++ b/src/companion.rs
@@ -1,7 +1,7 @@
 use crate::memory::Memory;
 use crate::game_formatter::{MemoryRarity, DiagnosisType};
 use serde::{Deserialize, Serialize};
-use chrono::{DateTime, Utc};
+use chrono::{DateTime, Utc, Datelike};
 
 /// コンパニオンキャラクター
 #[derive(Debug, Clone, Serialize, Deserialize)]
diff --git a/src/game_formatter.rs b/src/game_formatter.rs
index 86e84bf..9391949 100644
--- a/src/game_formatter.rs
+++ b/src/game_formatter.rs
@@ -1,5 +1,6 @@
 use crate::memory::Memory;
 use serde::{Deserialize, Serialize};
+use chrono::Datelike;
 
 /// メモリーのレア度
 #[derive(Debug, Clone, Serialize, Deserialize)]
diff --git a/src/memory.rs b/src/memory.rs
index 62f002c..fbae5d8 100644
--- a/src/memory.rs
+++ b/src/memory.rs
@@ -238,7 +238,7 @@ impl MemoryManager {
     // 優先度順に記憶を取得
     pub fn get_memories_by_priority(&self) -> Vec<&Memory> {
         let mut memories: Vec<_> = self.memories.values().collect();
-        memories.sort_by(|a, b| b.priority_score.cmp(&a.priority_score));
+        memories.sort_by(|a, b| b.priority_score.partial_cmp(&a.priority_score).unwrap_or(std::cmp::Ordering::Equal));
         memories
     }