diff --git a/packages/cosmwasm-stargate/src/cosmwasmclient.spec.ts b/packages/cosmwasm-stargate/src/cosmwasmclient.spec.ts
index bbd7cdf5..e0e15981 100644
--- a/packages/cosmwasm-stargate/src/cosmwasmclient.spec.ts
+++ b/packages/cosmwasm-stargate/src/cosmwasmclient.spec.ts
@@ -409,9 +409,8 @@ describe("CosmWasmClient", () => {
       assert(contract);
 
       const client = await CosmWasmClient.connect(wasmd.endpoint);
-      const { data } = await client.queryContractSmart(contract.address, { verifier: {} });
-      const parsedData = JSON.parse(fromAscii(data));
-      expect(parsedData).toEqual({ verifier: contract.initMsg.verifier });
+      const result = await client.queryContractSmart(contract.address, { verifier: {} });
+      expect(result).toEqual({ verifier: contract.initMsg.verifier });
     });
 
     it("errors for malformed query message", async () => {
diff --git a/packages/cosmwasm-stargate/src/queries/wasm.spec.ts b/packages/cosmwasm-stargate/src/queries/wasm.spec.ts
index a2696082..b251f4db 100644
--- a/packages/cosmwasm-stargate/src/queries/wasm.spec.ts
+++ b/packages/cosmwasm-stargate/src/queries/wasm.spec.ts
@@ -341,10 +341,8 @@ describe("WasmExtension", () => {
       assert(hackatomContractAddress);
       const client = await makeWasmClient(wasmd.endpoint);
       const request = { verifier: {} };
-      const { data } = await client.unverified.wasm.queryContractSmart(hackatomContractAddress, request);
-      assert(data);
-      const parsedData = JSON.parse(fromAscii(data));
-      expect(parsedData).toEqual({ verifier: alice.address0 });
+      const result = await client.unverified.wasm.queryContractSmart(hackatomContractAddress, request);
+      expect(result).toEqual({ verifier: alice.address0 });
     });
 
     it("throws for invalid query requests", async () => {
diff --git a/packages/cosmwasm-stargate/src/queries/wasm.ts b/packages/cosmwasm-stargate/src/queries/wasm.ts
index 40dc6728..1fd7db7b 100644
--- a/packages/cosmwasm-stargate/src/queries/wasm.ts
+++ b/packages/cosmwasm-stargate/src/queries/wasm.ts
@@ -1,5 +1,6 @@
 /* eslint-disable @typescript-eslint/naming-convention */
-import { toAscii } from "@cosmjs/encoding";
+import { JsonObject } from "@cosmjs/cosmwasm-launchpad";
+import { fromUtf8, toAscii } from "@cosmjs/encoding";
 import { QueryClient } from "@cosmjs/stargate";
 import Long from "long";
 
@@ -12,7 +13,6 @@ type IQueryContractHistoryResponse = cosmwasm.wasm.v1beta1.IQueryContractHistory
 type IQueryContractInfoResponse = cosmwasm.wasm.v1beta1.IQueryContractInfoResponse;
 type IQueryContractsByCodeResponse = cosmwasm.wasm.v1beta1.IQueryContractsByCodeResponse;
 type IQueryRawContractStateResponse = cosmwasm.wasm.v1beta1.IQueryRawContractStateResponse;
-type IQuerySmartContractStateResponse = cosmwasm.wasm.v1beta1.IQuerySmartContractStateResponse;
 
 const { Query } = cosmwasm.wasm.v1beta1;
 
@@ -61,10 +61,7 @@ export interface WasmExtension {
        * Makes a smart query on the contract and parses the response as JSON.
        * Throws error if no such contract exists, the query format is invalid or the response is invalid.
        */
-      readonly queryContractSmart: (
-        address: string,
-        query: Record<string, unknown>,
-      ) => Promise<IQuerySmartContractStateResponse>;
+      readonly queryContractSmart: (address: string, query: Record<string, unknown>) => Promise<JsonObject>;
     };
   };
 }
@@ -117,7 +114,13 @@ export function setupWasmExtension(base: QueryClient): WasmExtension {
 
         queryContractSmart: async (address: string, query: Record<string, unknown>) => {
           const request = { address: address, queryData: toAscii(JSON.stringify(query)) };
-          return queryService.smartContractState(request);
+          const { data } = await queryService.smartContractState(request);
+          // By convention, smart queries must return a valid JSON document (see https://github.com/CosmWasm/cosmwasm/issues/144)
+          try {
+            return JSON.parse(fromUtf8(data));
+          } catch (error) {
+            throw new Error("Contract did not return valid JSON data");
+          }
         },
       },
     },
diff --git a/packages/cosmwasm-stargate/types/queries/wasm.d.ts b/packages/cosmwasm-stargate/types/queries/wasm.d.ts
index 3b6c1249..c1f34a94 100644
--- a/packages/cosmwasm-stargate/types/queries/wasm.d.ts
+++ b/packages/cosmwasm-stargate/types/queries/wasm.d.ts
@@ -1,3 +1,4 @@
+import { JsonObject } from "@cosmjs/cosmwasm-launchpad";
 import { QueryClient } from "@cosmjs/stargate";
 import { cosmwasm } from "../codec";
 declare type IQueryAllContractStateResponse = cosmwasm.wasm.v1beta1.IQueryAllContractStateResponse;
@@ -7,7 +8,6 @@ declare type IQueryContractHistoryResponse = cosmwasm.wasm.v1beta1.IQueryContrac
 declare type IQueryContractInfoResponse = cosmwasm.wasm.v1beta1.IQueryContractInfoResponse;
 declare type IQueryContractsByCodeResponse = cosmwasm.wasm.v1beta1.IQueryContractsByCodeResponse;
 declare type IQueryRawContractStateResponse = cosmwasm.wasm.v1beta1.IQueryRawContractStateResponse;
-declare type IQuerySmartContractStateResponse = cosmwasm.wasm.v1beta1.IQuerySmartContractStateResponse;
 export interface WasmExtension {
   readonly unverified: {
     readonly wasm: {
@@ -53,10 +53,7 @@ export interface WasmExtension {
        * Makes a smart query on the contract and parses the response as JSON.
        * Throws error if no such contract exists, the query format is invalid or the response is invalid.
        */
-      readonly queryContractSmart: (
-        address: string,
-        query: Record<string, unknown>,
-      ) => Promise<IQuerySmartContractStateResponse>;
+      readonly queryContractSmart: (address: string, query: Record<string, unknown>) => Promise<JsonObject>;
     };
   };
 }