diff --git a/modules/4337/certora/specs/ValidationDataLastBitOne.spec b/modules/4337/certora/specs/ValidationDataLastBitOne.spec
index 094b58361..9f48e24bb 100644
--- a/modules/4337/certora/specs/ValidationDataLastBitOne.spec
+++ b/modules/4337/certora/specs/ValidationDataLastBitOne.spec
@@ -12,7 +12,7 @@ methods {
         Safe4337Module.PackedUserOperation userOp
     ) external returns(bytes32) envfree => PER_CALLEE_CONSTANT;
 
-    function _._checkSignatureLength(bytes calldata, uint256) internal returns(bool) => ALWAYS(true);
+    function _._checkSignatureLength(bytes calldata, uint256) internal => ALWAYS(true);
 }
 
 rule validationDataLastBitOneIfCheckSignaturesFails(address sender,