diff --git a/packages/cosmwasm-stargate/src/aminotypes.spec.ts b/packages/cosmwasm-stargate/src/aminotypes.spec.ts
index 5dabad68..7e193f0a 100644
--- a/packages/cosmwasm-stargate/src/aminotypes.spec.ts
+++ b/packages/cosmwasm-stargate/src/aminotypes.spec.ts
@@ -1,5 +1,5 @@
 /* eslint-disable @typescript-eslint/naming-convention */
-import { fromBase64, toUtf8 } from "@cosmjs/encoding";
+import { fromBase64, toBase64, toUtf8 } from "@cosmjs/encoding";
 import { AminoTypes, coins } from "@cosmjs/stargate";
 import {
   MsgClearAdmin,
@@ -64,7 +64,7 @@ describe("AminoTypes", () => {
             sender: "cosmos1pkptre7fdkl6gfrzlesjjvhxhlc3r4gmmk8rs6",
             code_id: "12345",
             label: "sticky",
-            msg: { foo: "bar" },
+            msg: toBase64(toUtf8(`{"foo":"bar"}`)),
             funds: coins(1234, "ucosm"),
             admin: "cosmos10dyr9899g6t0pelew4nvf4j5c3jcgv0r73qga5",
           },
@@ -92,7 +92,7 @@ describe("AminoTypes", () => {
             sender: "cosmos1pkptre7fdkl6gfrzlesjjvhxhlc3r4gmmk8rs6",
             code_id: "12345",
             label: "sticky",
-            msg: { foo: "bar" },
+            msg: toBase64(toUtf8(`{"foo":"bar"}`)),
             funds: coins(1234, "ucosm"),
             admin: undefined,
           },
@@ -230,7 +230,7 @@ describe("AminoTypes", () => {
             sender: "cosmos1pkptre7fdkl6gfrzlesjjvhxhlc3r4gmmk8rs6",
             code_id: "12345",
             label: "sticky",
-            msg: { foo: "bar" },
+            msg: toBase64(toUtf8(`{"foo":"bar"}`)),
             funds: coins(1234, "ucosm"),
             admin: "cosmos10dyr9899g6t0pelew4nvf4j5c3jcgv0r73qga5",
           },
@@ -258,7 +258,7 @@ describe("AminoTypes", () => {
             sender: "cosmos1pkptre7fdkl6gfrzlesjjvhxhlc3r4gmmk8rs6",
             code_id: "12345",
             label: "sticky",
-            msg: { foo: "bar" },
+            msg: toBase64(toUtf8(`{"foo":"bar"}`)),
             funds: coins(1234, "ucosm"),
           },
         };
diff --git a/packages/cosmwasm-stargate/src/aminotypes.ts b/packages/cosmwasm-stargate/src/aminotypes.ts
index 2865e7e5..1f9bc306 100644
--- a/packages/cosmwasm-stargate/src/aminotypes.ts
+++ b/packages/cosmwasm-stargate/src/aminotypes.ts
@@ -65,8 +65,8 @@ export interface AminoMsgInstantiateContract {
     readonly code_id: string;
     /** Human-readable label for this contract */
     readonly label: string;
-    /** Instantiate message as JavaScript object */
-    readonly msg: any;
+    /** Instantiate message as base64 encoded JSON */
+    readonly msg: string;
     readonly funds: readonly Coin[];
     /** Bech32-encoded admin address */
     readonly admin?: string;
@@ -150,7 +150,7 @@ export const cosmWasmTypes: Record<string, AminoConverter> = {
       sender: sender,
       code_id: codeId.toString(),
       label: label,
-      msg: JSON.parse(fromUtf8(msg)),
+      msg: toBase64(msg),
       funds: funds,
       admin: admin || undefined,
     }),
@@ -165,7 +165,7 @@ export const cosmWasmTypes: Record<string, AminoConverter> = {
       sender: sender,
       codeId: Long.fromString(code_id),
       label: label,
-      msg: toUtf8(JSON.stringify(msg)),
+      msg: fromBase64(msg),
       funds: [...funds],
       admin: admin ?? "",
     }),
diff --git a/packages/cosmwasm-stargate/src/signingcosmwasmclient.spec.ts b/packages/cosmwasm-stargate/src/signingcosmwasmclient.spec.ts
index 36c83460..dc66e3a6 100644
--- a/packages/cosmwasm-stargate/src/signingcosmwasmclient.spec.ts
+++ b/packages/cosmwasm-stargate/src/signingcosmwasmclient.spec.ts
@@ -34,6 +34,7 @@ import {
   defaultSigningClientOptions,
   defaultUpdateAdminFee,
   defaultUploadFee,
+  deployedHackatom,
   getHackatom,
   makeRandomAddress,
   makeWasmClient,
@@ -150,7 +151,7 @@ describe("SigningCosmWasmClient", () => {
       const options = { ...defaultSigningClientOptions, prefix: wasmd.prefix };
       const client = await SigningCosmWasmClient.connectWithSigner(wasmd.endpoint, wallet, options);
       const { codeId } = await client.upload(alice.address0, getHackatom().data, defaultUploadFee);
-      const contractAddress1 = await client.instantiate(
+      const { contractAddress: address1 } = await client.instantiate(
         alice.address0,
         codeId,
         {
@@ -160,7 +161,7 @@ describe("SigningCosmWasmClient", () => {
         "contract 1",
         defaultInstantiateFee,
       );
-      const contractAddress2 = await client.instantiate(
+      const { contractAddress: address2 } = await client.instantiate(
         alice.address0,
         codeId,
         {
@@ -170,7 +171,41 @@ describe("SigningCosmWasmClient", () => {
         "contract 2",
         defaultInstantiateFee,
       );
-      expect(contractAddress1).not.toEqual(contractAddress2);
+      expect(address1).not.toEqual(address2);
+      client.disconnect();
+    });
+
+    it("works with legacy Amino signer", async () => {
+      pendingWithoutWasmd();
+      const wallet = await Secp256k1HdWallet.fromMnemonic(alice.mnemonic, { prefix: wasmd.prefix });
+      const options = { ...defaultSigningClientOptions, prefix: wasmd.prefix };
+      const client = await SigningCosmWasmClient.connectWithSigner(wasmd.endpoint, wallet, options);
+
+      // With admin
+      await client.instantiate(
+        alice.address0,
+        deployedHackatom.codeId,
+        {
+          verifier: alice.address0,
+          beneficiary: makeRandomAddress(),
+        },
+        "contract 1",
+        defaultInstantiateFee,
+        { admin: makeRandomAddress() },
+      );
+
+      // Without admin
+      await client.instantiate(
+        alice.address0,
+        deployedHackatom.codeId,
+        {
+          verifier: alice.address0,
+          beneficiary: makeRandomAddress(),
+        },
+        "contract 1",
+        defaultInstantiateFee,
+      );
+
       client.disconnect();
     });
   });