diff --git a/src/splitter.rs b/src/splitter.rs
index b3147e1..ebf147c 100644
--- a/src/splitter.rs
+++ b/src/splitter.rs
@@ -1092,12 +1092,12 @@ fn best_feature_split_var_hess(
 ) {
     let split_info = unsafe { split_info_slice.get_mut(feat_idx) };
     split_info.split_gain = -1.0;
+    split_info.left_cats = HashSet::new();
+    split_info.right_cats = HashSet::new();
 
     let mut max_gain: Option<f32> = None;
     let mut generalization: Option<f32>;
-    let mut left_cats: HashSet<usize> = HashSet::new();
-    let mut right_cats: HashSet<usize> = HashSet::new();
-    let mut is_cat = false;
+    let mut all_cats: Vec<usize> = Vec::new();
 
     let evaluate_fn = eval_callables(false, create_missing_branch);
 
@@ -1108,12 +1108,11 @@ fn best_feature_split_var_hess(
 
     if let Some(c_index) = cat_index {
         if c_index.contains(&feature) {
-            is_cat = true;
             sort_cat_bins_by_stat(&mut hist, false);
-            right_cats = HashSet::from_iter(
-                hist.iter()
-                    .map(|b| unsafe { b.get().as_ref().unwrap().cut_value } as usize),
-            );
+            all_cats = hist
+                .iter()
+                .map(|b| unsafe { b.get().as_ref().unwrap().cut_value } as usize)
+                .collect();
         }
     }
 
@@ -1148,18 +1147,9 @@ fn best_feature_split_var_hess(
     let mut cuml_hessian_valid = [f32::ZERO; 5];
     let mut cuml_counts_valid = [0_usize; 5];
 
-    let mut cat: Option<usize> = None;
-
     for bin in hist {
         let b = unsafe { bin.get().as_ref().unwrap() };
 
-        if is_cat && cat.is_some() {
-            left_cats.insert(cat.unwrap());
-            right_cats.remove(&cat.unwrap());
-        }
-
-        cat = Some(b.cut_value as usize);
-
         let left_gradient_train = cuml_gradient_train;
         let left_hessian_train = cuml_hessian_train;
         let left_counts_train = cuml_counts_train;
@@ -1300,6 +1290,17 @@ fn best_feature_split_var_hess(
         if (max_gain.is_none() || split_gain > max_gain.unwrap()) && (generalization.is_some() || node.num == 0) {
             max_gain = Some(split_gain);
 
+            let mut left_cats: HashSet<usize> = HashSet::new();
+            let mut right_cats: HashSet<usize> = all_cats.iter().copied().collect();
+
+            for c in all_cats.iter() {
+                if *c == b.cut_value as usize {
+                    break;
+                }
+                left_cats.insert(*c);
+                right_cats.remove(c);
+            }
+
             split_info.split_gain = split_gain;
             split_info.split_feature = feature;
             split_info.split_value = b.cut_value;
@@ -1308,8 +1309,8 @@ fn best_feature_split_var_hess(
             split_info.right_node = right_node_info;
             split_info.missing_node = missing_info;
             split_info.generalization = generalization;
-            split_info.left_cats = left_cats.clone();
-            split_info.right_cats = right_cats.clone();
+            split_info.left_cats = left_cats;
+            split_info.right_cats = right_cats;
         }
     }
 }