diff --git a/contracts/root/predicates/IPredicate.sol b/contracts/root/predicates/IPredicate.sol
index 9b50f8f66..a3c107607 100644
--- a/contracts/root/predicates/IPredicate.sol
+++ b/contracts/root/predicates/IPredicate.sol
@@ -96,6 +96,7 @@ contract PredicateUtils is ExitsDataStructure, ChainIdMixin {
             bytes32(txList[7].toUint()),
             bytes32(txList[8].toUint())
         );
+        require(signer != address(0), "Invalid signer");
     }
 
     function decodeExit(bytes memory data)