diff --git a/parser/src/ffi_par.rs b/parser/src/ffi_par.rs
index 8482978..b871180 100644
--- a/parser/src/ffi_par.rs
+++ b/parser/src/ffi_par.rs
@@ -11,32 +11,35 @@ fn par_compute_mask_inner(constraints: Vec<LlgConstraintStep>) {
 
         let cc = unsafe { &mut *step.constraint };
         if let Some(constraint) = &mut cc.constraint {
+            let mut num_copied = 0;
+            let mut add_eos = false;
+            let eos = constraint.tok_trie().eos_token() as usize;
             match constraint.compute_mask() {
                 Ok(r) => {
-                    let mut num_copied = 0;
                     if let Some(m) = r.sample_mask.as_ref() {
                         num_copied = std::cmp::min(m.len(), mask_elts);
                         unsafe {
                             std::ptr::copy_nonoverlapping(m.as_ptr(), step.mask_dest, num_copied);
                         }
                     }
-                    let left = mask_elts - num_copied;
-                    if left > 0 {
-                        unsafe {
-                            std::ptr::write_bytes(step.mask_dest.add(num_copied), 0, left);
-                        }
-                    }
-                    if r.is_stop() {
-                        let eos = constraint.tok_trie().eos_token() as usize;
-                        if eos / 32 < mask_elts {
-                            unsafe {
-                                *step.mask_dest.add(eos / 32) |= 1 << (eos % 32);
-                            }
-                        }
-                    }
+                    add_eos = r.is_stop();
                 }
                 Err(e) => cc.set_error(&e.to_string()),
             }
+
+            let left = mask_elts - num_copied;
+            if left > 0 {
+                unsafe {
+                    std::ptr::write_bytes(step.mask_dest.add(num_copied), 0, left);
+                }
+            }
+            if add_eos {
+                if eos / 32 < mask_elts {
+                    unsafe {
+                        *step.mask_dest.add(eos / 32) |= 1 << (eos % 32);
+                    }
+                }
+            }
         }
     });
 }