diff --git a/plonky2/src/gates/lookup.rs b/plonky2/src/gates/lookup.rs
index 7069113b..2bd3e60f 100644
--- a/plonky2/src/gates/lookup.rs
+++ b/plonky2/src/gates/lookup.rs
@@ -201,8 +201,14 @@ impl<F: RichField + Extendable<D>, const D: usize> SimpleGenerator<F, D> for Loo
         let get_wire = |wire: usize| -> F { witness.get_target(Target::wire(self.row, wire)) };
 
         let input_val = get_wire(LookupGate::wire_ith_looking_inp(self.slot_nb));
-        let (input, output) = self.lut[input_val.to_canonical_u64() as usize];
-        if input_val == F::from_canonical_u16(input) {
+        let idx_candidate: usize = input_val.to_canonical_u64() as usize;
+        let ((input, output), ok) = if idx_candidate < self.lut.len() {
+            (self.lut[idx_candidate], true)
+        } 
+        else {
+            ((0,0), false)
+        };
+        if ok && (input_val == F::from_canonical_u16(input)) {
             let output_val = F::from_canonical_u16(output);
 
             let out_wire = Target::wire(self.row, LookupGate::wire_ith_looking_out(self.slot_nb));