diff --git a/packages/cosmwasm/src/lcdapi/wasm.ts b/packages/cosmwasm/src/lcdapi/wasm.ts
index 6c836744..521faeb6 100644
--- a/packages/cosmwasm/src/lcdapi/wasm.ts
+++ b/packages/cosmwasm/src/lcdapi/wasm.ts
@@ -1,5 +1,5 @@
 import { fromBase64, fromUtf8, toHex, toUtf8 } from "@cosmjs/encoding";
-import { LcdApiArray, LcdClient, LcdExtension, normalizeLcdApiArray } from "@cosmjs/sdk38";
+import { LcdApiArray, LcdClient, normalizeLcdApiArray } from "@cosmjs/sdk38";
 
 import { JsonObject, Model, parseWasmData, WasmData } from "../types";
 
@@ -75,7 +75,7 @@ function unwrapWasmResponse<T>(response: WasmResponse<T>): T {
 /**
  * @see https://github.com/cosmwasm/wasmd/blob/master/x/wasm/client/rest/query.go#L19-L27
  */
-export interface WasmExtension extends LcdExtension {
+export interface WasmExtension {
   readonly wasm: {
     readonly listCodeInfo: () => Promise<readonly CodeInfo[]>;
 
diff --git a/packages/cosmwasm/types/lcdapi/wasm.d.ts b/packages/cosmwasm/types/lcdapi/wasm.d.ts
index 5e454691..8859ffad 100644
--- a/packages/cosmwasm/types/lcdapi/wasm.d.ts
+++ b/packages/cosmwasm/types/lcdapi/wasm.d.ts
@@ -1,4 +1,4 @@
-import { LcdClient, LcdExtension } from "@cosmjs/sdk38";
+import { LcdClient } from "@cosmjs/sdk38";
 import { JsonObject, Model } from "../types";
 export interface CodeInfo {
   readonly id: number;
@@ -40,7 +40,7 @@ export interface ContractDetails extends ContractInfo {
 /**
  * @see https://github.com/cosmwasm/wasmd/blob/master/x/wasm/client/rest/query.go#L19-L27
  */
-export interface WasmExtension extends LcdExtension {
+export interface WasmExtension {
   readonly wasm: {
     readonly listCodeInfo: () => Promise<readonly CodeInfo[]>;
     /**
diff --git a/packages/sdk38/src/index.ts b/packages/sdk38/src/index.ts
index 6e9e6acf..d6053e6e 100644
--- a/packages/sdk38/src/index.ts
+++ b/packages/sdk38/src/index.ts
@@ -27,7 +27,6 @@ export {
   BroadcastMode,
   EncodeTxResponse,
   LcdApiArray,
-  LcdExtension,
   LcdClient,
   NodeInfoResponse,
   normalizeLcdApiArray,
diff --git a/packages/sdk38/src/lcdapi/auth.ts b/packages/sdk38/src/lcdapi/auth.ts
index 6ba13a63..d9066733 100644
--- a/packages/sdk38/src/lcdapi/auth.ts
+++ b/packages/sdk38/src/lcdapi/auth.ts
@@ -1,5 +1,5 @@
 import { Coin } from "../coins";
-import { LcdClient, LcdExtension } from "./lcdclient";
+import { LcdClient } from "./lcdclient";
 
 export interface CosmosSdkAccount {
   /** Bech32 account address */
@@ -19,7 +19,7 @@ export interface AuthAccountsResponse {
   };
 }
 
-export interface AuthExtension extends LcdExtension {
+export interface AuthExtension {
   readonly auth: {
     readonly account: (address: string) => Promise<AuthAccountsResponse>;
   };
diff --git a/packages/sdk38/src/lcdapi/index.ts b/packages/sdk38/src/lcdapi/index.ts
index 96e2c8b6..bc39d863 100644
--- a/packages/sdk38/src/lcdapi/index.ts
+++ b/packages/sdk38/src/lcdapi/index.ts
@@ -18,4 +18,4 @@ export {
   SearchTxsResponse,
   TxsResponse,
 } from "./base";
-export { LcdApiArray, LcdClient, LcdExtension, normalizeLcdApiArray } from "./lcdclient";
+export { LcdApiArray, LcdClient, normalizeLcdApiArray } from "./lcdclient";
diff --git a/packages/sdk38/src/lcdapi/lcdclient.spec.ts b/packages/sdk38/src/lcdapi/lcdclient.spec.ts
index 97bf9990..2a35ee24 100644
--- a/packages/sdk38/src/lcdapi/lcdclient.spec.ts
+++ b/packages/sdk38/src/lcdapi/lcdclient.spec.ts
@@ -23,7 +23,7 @@ import {
 import { StdFee } from "../types";
 import { setupAuthExtension } from "./auth";
 import { TxsResponse } from "./base";
-import { LcdApiArray, LcdClient, LcdExtension, normalizeLcdApiArray } from "./lcdclient";
+import { LcdApiArray, LcdClient, normalizeLcdApiArray } from "./lcdclient";
 
 /** Deployed as part of scripts/wasmd/init.sh */
 export const deployedErc20 = {
@@ -79,7 +79,7 @@ describe("LcdClient", () => {
       return response.result;
     }
 
-    interface WasmExtension extends LcdExtension {
+    interface WasmExtension {
       wasm: {
         listCodeInfo: () => Promise<readonly CodeInfo[]>;
       };
diff --git a/packages/sdk38/src/lcdapi/lcdclient.ts b/packages/sdk38/src/lcdapi/lcdclient.ts
index 1d82478f..d1685b68 100644
--- a/packages/sdk38/src/lcdapi/lcdclient.ts
+++ b/packages/sdk38/src/lcdapi/lcdclient.ts
@@ -20,9 +20,7 @@ export function normalizeLcdApiArray<T>(backend: LcdApiArray<T>): readonly T[] {
   return backend || [];
 }
 
-export type LcdExtension = Record<string, Record<string, (...args: any[]) => any>>;
-
-type LcdExtensionSetup<P extends LcdExtension> = (base: LcdClient) => P;
+type LcdExtensionSetup<P> = (base: LcdClient) => P;
 
 export interface LcdClientBaseOptions {
   readonly apiUrl: string;
@@ -68,20 +66,20 @@ export class LcdClient {
   public static withExtensions(options: LcdClientBaseOptions): LcdClient;
 
   /** Constructs an LCD client with 1 extension */
-  public static withExtensions<A extends LcdExtension>(
+  public static withExtensions<A extends object>(
     options: LcdClientBaseOptions,
     setupExtensionA: LcdExtensionSetup<A>,
   ): LcdClient & A;
 
   /** Constructs an LCD client with 2 extensions */
-  public static withExtensions<A extends LcdExtension, B extends LcdExtension>(
+  public static withExtensions<A extends object, B extends object>(
     options: LcdClientBaseOptions,
     setupExtensionA: LcdExtensionSetup<A>,
     setupExtensionB: LcdExtensionSetup<B>,
   ): LcdClient & A & B;
 
   /** Constructs an LCD client with 3 extensions */
-  public static withExtensions<A extends LcdExtension, B extends LcdExtension, C extends LcdExtension>(
+  public static withExtensions<A extends object, B extends object, C extends object>(
     options: LcdClientBaseOptions,
     setupExtensionA: LcdExtensionSetup<A>,
     setupExtensionB: LcdExtensionSetup<B>,
@@ -89,12 +87,7 @@ export class LcdClient {
   ): LcdClient & A & B & C;
 
   /** Constructs an LCD client with 4 extensions */
-  public static withExtensions<
-    A extends LcdExtension,
-    B extends LcdExtension,
-    C extends LcdExtension,
-    D extends LcdExtension
-  >(
+  public static withExtensions<A extends object, B extends object, C extends object, D extends object>(
     options: LcdClientBaseOptions,
     setupExtensionA: LcdExtensionSetup<A>,
     setupExtensionB: LcdExtensionSetup<B>,
@@ -104,11 +97,11 @@ export class LcdClient {
 
   /** Constructs an LCD client with 5 extensions */
   public static withExtensions<
-    A extends LcdExtension,
-    B extends LcdExtension,
-    C extends LcdExtension,
-    D extends LcdExtension,
-    E extends LcdExtension
+    A extends object,
+    B extends object,
+    C extends object,
+    D extends object,
+    E extends object
   >(
     options: LcdClientBaseOptions,
     setupExtensionA: LcdExtensionSetup<A>,
@@ -120,12 +113,12 @@ export class LcdClient {
 
   /** Constructs an LCD client with 6 extensions */
   public static withExtensions<
-    A extends LcdExtension,
-    B extends LcdExtension,
-    C extends LcdExtension,
-    D extends LcdExtension,
-    E extends LcdExtension,
-    F extends LcdExtension
+    A extends object,
+    B extends object,
+    C extends object,
+    D extends object,
+    E extends object,
+    F extends object
   >(
     options: LcdClientBaseOptions,
     setupExtensionA: LcdExtensionSetup<A>,
@@ -138,13 +131,13 @@ export class LcdClient {
 
   /** Constructs an LCD client with 7 extensions */
   public static withExtensions<
-    A extends LcdExtension,
-    B extends LcdExtension,
-    C extends LcdExtension,
-    D extends LcdExtension,
-    E extends LcdExtension,
-    F extends LcdExtension,
-    G extends LcdExtension
+    A extends object,
+    B extends object,
+    C extends object,
+    D extends object,
+    E extends object,
+    F extends object,
+    G extends object
   >(
     options: LcdClientBaseOptions,
     setupExtensionA: LcdExtensionSetup<A>,
@@ -158,14 +151,14 @@ export class LcdClient {
 
   /** Constructs an LCD client with 8 extensions */
   public static withExtensions<
-    A extends LcdExtension,
-    B extends LcdExtension,
-    C extends LcdExtension,
-    D extends LcdExtension,
-    E extends LcdExtension,
-    F extends LcdExtension,
-    G extends LcdExtension,
-    H extends LcdExtension
+    A extends object,
+    B extends object,
+    C extends object,
+    D extends object,
+    E extends object,
+    F extends object,
+    G extends object,
+    H extends object
   >(
     options: LcdClientBaseOptions,
     setupExtensionA: LcdExtensionSetup<A>,
@@ -179,14 +172,14 @@ export class LcdClient {
   ): LcdClient & A & B & C & D & E & F & G & H;
 
   public static withExtensions<
-    A extends LcdExtension,
-    B extends LcdExtension,
-    C extends LcdExtension,
-    D extends LcdExtension,
-    E extends LcdExtension,
-    F extends LcdExtension,
-    G extends LcdExtension,
-    H extends LcdExtension
+    A extends object,
+    B extends object,
+    C extends object,
+    D extends object,
+    E extends object,
+    F extends object,
+    G extends object,
+    H extends object
   >(
     options: LcdClientBaseOptions,
     setupExtensionA?: LcdExtensionSetup<A>,
@@ -200,7 +193,7 @@ export class LcdClient {
   ): any {
     const client = new LcdClient(options.apiUrl, options.broadcastMode);
 
-    const extensions = new Array<LcdExtension>();
+    const extensions = new Array<object>();
     if (setupExtensionA) extensions.push(setupExtensionA(client));
     if (setupExtensionB) extensions.push(setupExtensionB(client));
     if (setupExtensionC) extensions.push(setupExtensionC(client));
@@ -211,9 +204,8 @@ export class LcdClient {
     if (setupExtensionH) extensions.push(setupExtensionH(client));
     for (const extension of extensions) {
       assert(isNonNullObject(extension), `Extension must be a non-null object`);
-      for (const key in extension) {
-        assert(typeof key == "string", `Found non-string extension key: ${key}`);
-        (client as any)[key] = extension[key];
+      for (const [key, value] of Object.entries(extension)) {
+        (client as any)[key] = value;
       }
     }
 
diff --git a/packages/sdk38/src/lcdapi/supply.ts b/packages/sdk38/src/lcdapi/supply.ts
index a0bfb77a..06443134 100644
--- a/packages/sdk38/src/lcdapi/supply.ts
+++ b/packages/sdk38/src/lcdapi/supply.ts
@@ -1,5 +1,5 @@
 import { Coin } from "../coins";
-import { LcdApiArray, LcdClient, LcdExtension } from "./lcdclient";
+import { LcdApiArray, LcdClient } from "./lcdclient";
 
 export interface TotalSupplyAllReponse {
   readonly height: string;
@@ -12,7 +12,7 @@ export interface TotalSupplyReponse {
   readonly result: string;
 }
 
-export interface SupplyExtension extends LcdExtension {
+export interface SupplyExtension {
   readonly supply: {
     readonly totalAll: () => Promise<TotalSupplyAllReponse>;
     readonly total: (denom: string) => Promise<TotalSupplyReponse>;
diff --git a/packages/sdk38/types/index.d.ts b/packages/sdk38/types/index.d.ts
index fe93970c..38123a21 100644
--- a/packages/sdk38/types/index.d.ts
+++ b/packages/sdk38/types/index.d.ts
@@ -25,7 +25,6 @@ export {
   BroadcastMode,
   EncodeTxResponse,
   LcdApiArray,
-  LcdExtension,
   LcdClient,
   NodeInfoResponse,
   normalizeLcdApiArray,
diff --git a/packages/sdk38/types/lcdapi/auth.d.ts b/packages/sdk38/types/lcdapi/auth.d.ts
index 23ecb851..95f404d3 100644
--- a/packages/sdk38/types/lcdapi/auth.d.ts
+++ b/packages/sdk38/types/lcdapi/auth.d.ts
@@ -1,5 +1,5 @@
 import { Coin } from "../coins";
-import { LcdClient, LcdExtension } from "./lcdclient";
+import { LcdClient } from "./lcdclient";
 export interface CosmosSdkAccount {
   /** Bech32 account address */
   readonly address: string;
@@ -16,7 +16,7 @@ export interface AuthAccountsResponse {
     readonly value: CosmosSdkAccount;
   };
 }
-export interface AuthExtension extends LcdExtension {
+export interface AuthExtension {
   readonly auth: {
     readonly account: (address: string) => Promise<AuthAccountsResponse>;
   };
diff --git a/packages/sdk38/types/lcdapi/index.d.ts b/packages/sdk38/types/lcdapi/index.d.ts
index ad1eb321..dc0274a9 100644
--- a/packages/sdk38/types/lcdapi/index.d.ts
+++ b/packages/sdk38/types/lcdapi/index.d.ts
@@ -9,4 +9,4 @@ export {
   SearchTxsResponse,
   TxsResponse,
 } from "./base";
-export { LcdApiArray, LcdClient, LcdExtension, normalizeLcdApiArray } from "./lcdclient";
+export { LcdApiArray, LcdClient, normalizeLcdApiArray } from "./lcdclient";
diff --git a/packages/sdk38/types/lcdapi/lcdclient.d.ts b/packages/sdk38/types/lcdapi/lcdclient.d.ts
index 6df6dc3a..009e556e 100644
--- a/packages/sdk38/types/lcdapi/lcdclient.d.ts
+++ b/packages/sdk38/types/lcdapi/lcdclient.d.ts
@@ -11,8 +11,7 @@ import {
 /** Unfortunately, Cosmos SDK encodes empty arrays as null */
 export declare type LcdApiArray<T> = readonly T[] | null;
 export declare function normalizeLcdApiArray<T>(backend: LcdApiArray<T>): readonly T[];
-export declare type LcdExtension = Record<string, Record<string, (...args: any[]) => any>>;
-declare type LcdExtensionSetup<P extends LcdExtension> = (base: LcdClient) => P;
+declare type LcdExtensionSetup<P> = (base: LcdClient) => P;
 export interface LcdClientBaseOptions {
   readonly apiUrl: string;
   readonly broadcastMode?: BroadcastMode;
@@ -33,30 +32,25 @@ export declare class LcdClient {
   /** Constructs an LCD client with 0 extensions */
   static withExtensions(options: LcdClientBaseOptions): LcdClient;
   /** Constructs an LCD client with 1 extension */
-  static withExtensions<A extends LcdExtension>(
+  static withExtensions<A extends object>(
     options: LcdClientBaseOptions,
     setupExtensionA: LcdExtensionSetup<A>,
   ): LcdClient & A;
   /** Constructs an LCD client with 2 extensions */
-  static withExtensions<A extends LcdExtension, B extends LcdExtension>(
+  static withExtensions<A extends object, B extends object>(
     options: LcdClientBaseOptions,
     setupExtensionA: LcdExtensionSetup<A>,
     setupExtensionB: LcdExtensionSetup<B>,
   ): LcdClient & A & B;
   /** Constructs an LCD client with 3 extensions */
-  static withExtensions<A extends LcdExtension, B extends LcdExtension, C extends LcdExtension>(
+  static withExtensions<A extends object, B extends object, C extends object>(
     options: LcdClientBaseOptions,
     setupExtensionA: LcdExtensionSetup<A>,
     setupExtensionB: LcdExtensionSetup<B>,
     setupExtensionC: LcdExtensionSetup<C>,
   ): LcdClient & A & B & C;
   /** Constructs an LCD client with 4 extensions */
-  static withExtensions<
-    A extends LcdExtension,
-    B extends LcdExtension,
-    C extends LcdExtension,
-    D extends LcdExtension
-  >(
+  static withExtensions<A extends object, B extends object, C extends object, D extends object>(
     options: LcdClientBaseOptions,
     setupExtensionA: LcdExtensionSetup<A>,
     setupExtensionB: LcdExtensionSetup<B>,
@@ -65,11 +59,11 @@ export declare class LcdClient {
   ): LcdClient & A & B & C & D;
   /** Constructs an LCD client with 5 extensions */
   static withExtensions<
-    A extends LcdExtension,
-    B extends LcdExtension,
-    C extends LcdExtension,
-    D extends LcdExtension,
-    E extends LcdExtension
+    A extends object,
+    B extends object,
+    C extends object,
+    D extends object,
+    E extends object
   >(
     options: LcdClientBaseOptions,
     setupExtensionA: LcdExtensionSetup<A>,
@@ -80,12 +74,12 @@ export declare class LcdClient {
   ): LcdClient & A & B & C & D & E;
   /** Constructs an LCD client with 6 extensions */
   static withExtensions<
-    A extends LcdExtension,
-    B extends LcdExtension,
-    C extends LcdExtension,
-    D extends LcdExtension,
-    E extends LcdExtension,
-    F extends LcdExtension
+    A extends object,
+    B extends object,
+    C extends object,
+    D extends object,
+    E extends object,
+    F extends object
   >(
     options: LcdClientBaseOptions,
     setupExtensionA: LcdExtensionSetup<A>,
@@ -97,13 +91,13 @@ export declare class LcdClient {
   ): LcdClient & A & B & C & D & E & F;
   /** Constructs an LCD client with 7 extensions */
   static withExtensions<
-    A extends LcdExtension,
-    B extends LcdExtension,
-    C extends LcdExtension,
-    D extends LcdExtension,
-    E extends LcdExtension,
-    F extends LcdExtension,
-    G extends LcdExtension
+    A extends object,
+    B extends object,
+    C extends object,
+    D extends object,
+    E extends object,
+    F extends object,
+    G extends object
   >(
     options: LcdClientBaseOptions,
     setupExtensionA: LcdExtensionSetup<A>,
@@ -116,14 +110,14 @@ export declare class LcdClient {
   ): LcdClient & A & B & C & D & E & F & G;
   /** Constructs an LCD client with 8 extensions */
   static withExtensions<
-    A extends LcdExtension,
-    B extends LcdExtension,
-    C extends LcdExtension,
-    D extends LcdExtension,
-    E extends LcdExtension,
-    F extends LcdExtension,
-    G extends LcdExtension,
-    H extends LcdExtension
+    A extends object,
+    B extends object,
+    C extends object,
+    D extends object,
+    E extends object,
+    F extends object,
+    G extends object,
+    H extends object
   >(
     options: LcdClientBaseOptions,
     setupExtensionA: LcdExtensionSetup<A>,
diff --git a/packages/sdk38/types/lcdapi/supply.d.ts b/packages/sdk38/types/lcdapi/supply.d.ts
index 4b45aeb7..e9bf1d2c 100644
--- a/packages/sdk38/types/lcdapi/supply.d.ts
+++ b/packages/sdk38/types/lcdapi/supply.d.ts
@@ -1,5 +1,5 @@
 import { Coin } from "../coins";
-import { LcdApiArray, LcdClient, LcdExtension } from "./lcdclient";
+import { LcdApiArray, LcdClient } from "./lcdclient";
 export interface TotalSupplyAllReponse {
   readonly height: string;
   readonly result: LcdApiArray<Coin>;
@@ -9,7 +9,7 @@ export interface TotalSupplyReponse {
   /** The amount */
   readonly result: string;
 }
-export interface SupplyExtension extends LcdExtension {
+export interface SupplyExtension {
   readonly supply: {
     readonly totalAll: () => Promise<TotalSupplyAllReponse>;
     readonly total: (denom: string) => Promise<TotalSupplyReponse>;