diff --git a/src/engine/search.rs b/src/engine/search.rs
index 3e28c40..1265280 100644
--- a/src/engine/search.rs
+++ b/src/engine/search.rs
@@ -55,7 +55,7 @@ pub struct SolveObj {
     pub evaluator: Arc<Evaluator>,
     pub last_cache: Arc<LastCache>,
     pub params: SearchParams,
-    pub cache_gen: u8,
+    pub cache_gen: u32,
 }
 
 impl SolveObj {
@@ -64,7 +64,7 @@ impl SolveObj {
         eval_cache: Arc<EvalCacheTable>,
         evaluator: Arc<Evaluator>,
         params: SearchParams,
-        cache_gen: u8,
+        cache_gen: u32,
     ) -> SolveObj {
         SolveObj {
             res_cache,
diff --git a/src/engine/table.rs b/src/engine/table.rs
index 0b2f3cc..835c9ec 100644
--- a/src/engine/table.rs
+++ b/src/engine/table.rs
@@ -17,7 +17,7 @@ pub struct EvalCache {
     pub board: Board,
     pub lower: i16,
     pub upper: i16,
-    pub gen: u8,
+    pub gen: u32,
     pub best: Option<Hand>,
     pub depth: i32,
 }
@@ -77,7 +77,7 @@ pub struct ResCache {
     pub board: Board,
     pub lower: i8,
     pub upper: i8,
-    pub gen: u8,
+    pub gen: u32,
     pub best: Option<Hand>,
 }
 
@@ -198,7 +198,7 @@ pub type EvalCacheTable = CacheTable<EvalCache>;
 pub type ResCacheTable = CacheTable<ResCache>;
 
 fn make_record(
-    gen: u8,
+    gen: u32,
     board: Board,
     mut res: i8,
     best: Option<Hand>,
@@ -224,7 +224,7 @@ fn make_record(
 
 pub fn update_table(
     res_cache: Arc<ResCacheTable>,
-    cache_gen: u8,
+    cache_gen: u32,
     board: Board,
     res: i8,
     best: Option<Hand>,
diff --git a/src/engine/think.rs b/src/engine/think.rs
index 9832e64..08b014c 100644
--- a/src/engine/think.rs
+++ b/src/engine/think.rs
@@ -23,7 +23,7 @@ pub struct Searcher {
     pub cache: Arc<EvalCacheTable>,
     pub timer: Option<Timer>,
     pub node_count: usize,
-    pub cache_gen: u8,
+    pub cache_gen: u32,
 }
 
 pub const DEPTH_SCALE: i32 = 256;