diff --git a/parser/src/earley/slicer.rs b/parser/src/earley/slicer.rs
index bf1b0dd..6d24053 100644
--- a/parser/src/earley/slicer.rs
+++ b/parser/src/earley/slicer.rs
@@ -88,6 +88,7 @@ impl SlicedBiasComputer {
                         tokens.push(vec![]);
                     }
                 }
+                mask.trim_trailing_zeros();
             }
 
             let entry = TokenizerSlice {
diff --git a/toktrie/src/svob.rs b/toktrie/src/svob.rs
index ef65a46..faaad56 100644
--- a/toktrie/src/svob.rs
+++ b/toktrie/src/svob.rs
@@ -289,12 +289,23 @@ impl SimpleVob {
     }
 
     pub fn or(&mut self, other: &SimpleVob) {
-        assert_eq!(self.size, other.size);
+        assert!(self.size >= other.size);
         for (idx, v) in self.data.iter_mut().zip(other.data.iter()) {
             *idx |= *v;
         }
     }
 
+    pub fn trim_trailing_zeros(&mut self) {
+        let mut idx = self.data.len();
+        while idx > 0 && self.data[idx - 1] == 0 {
+            idx -= 1;
+        }
+        if self.data.len() != idx {
+            self.data.truncate(idx);
+            self.size = self.data.len() * BITS;
+        }
+    }
+
     /// self |= other & !minus
     pub fn or_minus(&mut self, other: &SimpleVob, minus: &SimpleVob) {
         assert_eq!(self.size, other.size);