diff --git a/circuits/mimcsponge.circom b/circuits/mimcsponge.circom
index de9bf1e..3e84c46 100644
--- a/circuits/mimcsponge.circom
+++ b/circuits/mimcsponge.circom
@@ -21,7 +21,7 @@ template MiMCSponge(nInputs, nRounds, nOutputs) {
     }
   }
 
-  outs[0] = S[nInputs - 1].xL_out;
+  outs[0] <== S[nInputs - 1].xL_out;
 
   for (var i = 0; i < nOutputs - 1; i++) {
     S[nInputs + i] = MiMCFeistel(nRounds);