diff --git a/packages/neon-core/src/rpc/Query.ts b/packages/neon-core/src/rpc/Query.ts
index da08f291..e882e70f 100644
--- a/packages/neon-core/src/rpc/Query.ts
+++ b/packages/neon-core/src/rpc/Query.ts
@@ -5,6 +5,7 @@ import {
   ContractParam,
   StackItemJson,
   NEFJson,
+  isContractParam,
 } from "../sc";
 import { BlockJson, Validator, BlockHeaderJson } from "../types";
 import { HexString } from "../u";
@@ -573,7 +574,7 @@ export class Query<TParams extends JsonRpcParams, TResponse> {
       params: [
         scriptHash,
         operation,
-        params.map((p) => (p instanceof ContractParam ? p.toJson() : p)),
+        params.map((p) => (isContractParam(p) ? p.toJson() : p)),
         signers.map((s) => (s instanceof Signer ? s.toJson() : s)),
       ],
     });
diff --git a/packages/neon-core/src/sc/ContractParam.ts b/packages/neon-core/src/sc/ContractParam.ts
index df84de45..a717aedf 100644
--- a/packages/neon-core/src/sc/ContractParam.ts
+++ b/packages/neon-core/src/sc/ContractParam.ts
@@ -502,3 +502,18 @@ export function likeContractParam(
     cp.value !== undefined
   );
 }
+
+// eslint-disable-next-line
+export function isContractParam(value: any): value is ContractParam {
+  if (value instanceof ContractParam) {
+    return true;
+  }
+
+  return (
+    value.type !== undefined &&
+    value.type in ContractParamType &&
+    value.value !== null &&
+    value.value !== undefined &&
+    typeof value.toJson === "function"
+  );
+}