diff --git a/packages/tendermint-rpc/src/rpcclients/httpclient.spec.ts b/packages/tendermint-rpc/src/rpcclients/httpclient.spec.ts
index 66295e3379..1c32650843 100644
--- a/packages/tendermint-rpc/src/rpcclients/httpclient.spec.ts
+++ b/packages/tendermint-rpc/src/rpcclients/httpclient.spec.ts
@@ -1,3 +1,4 @@
+/* eslint-disable @typescript-eslint/naming-convention */
 import { createJsonRpcRequest } from "../jsonrpc";
 import { defaultInstance } from "../testutil.spec";
 import { http, HttpClient } from "./httpclient";
@@ -8,7 +9,14 @@ function pendingWithoutTendermint(): void {
   }
 }
 
+function pendingWithoutHttpServer(): void {
+  if (!process.env.HTTPSERVER_ENABLED) {
+    pending("Set HTTPSERVER_ENABLED to enable HTTP tests");
+  }
+}
+
 const tendermintUrl = defaultInstance.url;
+const echoUrl = "http://localhost:5555/echo_headers";
 
 describe("http", () => {
   it("can send a health request", async () => {
@@ -22,6 +30,42 @@ describe("http", () => {
       http("POST", `http://localhost:56745`, undefined, createJsonRpcRequest("health")),
     ).toBeRejectedWithError(/(ECONNREFUSED|Failed to fetch)/i);
   });
+
+  it("can send custom headers", async () => {
+    pendingWithoutHttpServer();
+    // Without custom headers
+    const response1 = await http("POST", echoUrl, undefined, createJsonRpcRequest("health"));
+    expect(response1).toEqual({
+      request_headers: jasmine.objectContaining({
+        // Basic headers from http client
+        Accept: jasmine.any(String),
+        "Content-Length": jasmine.any(String),
+        "Content-Type": "application/json",
+        Host: jasmine.any(String),
+        "User-Agent": jasmine.any(String),
+      }),
+    });
+
+    // With custom headers
+    const response2 = await http(
+      "POST",
+      echoUrl,
+      { foo: "bar123", Authorization: "Basic Z3Vlc3Q6bm9QYXNzMTIz" },
+      createJsonRpcRequest("health"),
+    );
+    expect(response2).toEqual({
+      request_headers: jasmine.objectContaining({
+        // Basic headers from http client
+        "Content-Length": jasmine.any(String),
+        "Content-Type": "application/json",
+        Host: jasmine.any(String),
+        "User-Agent": jasmine.any(String),
+        // Custom headers
+        foo: "bar123",
+        Authorization: "Basic Z3Vlc3Q6bm9QYXNzMTIz",
+      }),
+    });
+  });
 });
 
 describe("HttpClient", () => {
diff --git a/packages/tendermint-rpc/src/rpcclients/httpclient.ts b/packages/tendermint-rpc/src/rpcclients/httpclient.ts
index 83dd81bb93..0b7dedacb4 100644
--- a/packages/tendermint-rpc/src/rpcclients/httpclient.ts
+++ b/packages/tendermint-rpc/src/rpcclients/httpclient.ts
@@ -11,8 +11,6 @@ import { hasProtocol, RpcClient } from "./rpcclient";
 // Global symbols in some environments
 // https://developer.mozilla.org/en-US/docs/Web/API/WindowOrWorkerGlobalScope/fetch
 declare const fetch: any | undefined;
-// eslint-disable-next-line @typescript-eslint/naming-convention
-declare const Headers: any | undefined;
 
 function filterBadStatus(res: any): any {
   if (res.status >= 400) {
@@ -34,11 +32,14 @@ export async function http(
   request?: any,
 ): Promise<any> {
   if (typeof fetch !== "undefined") {
-    const body = request ? JSON.stringify(request) : undefined;
     const settings = {
       method: method,
-      body: body,
-      headers: headers ? new Headers(headers) : undefined,
+      body: request ? JSON.stringify(request) : undefined,
+      headers: {
+        // eslint-disable-next-line @typescript-eslint/naming-convention
+        "Content-Type": "application/json",
+        ...headers,
+      },
     };
     return fetch(url, settings)
       .then(filterBadStatus)
diff --git a/packages/tendermint-rpc/webpack.web.config.js b/packages/tendermint-rpc/webpack.web.config.js
index 260f315444..d72c8f897f 100644
--- a/packages/tendermint-rpc/webpack.web.config.js
+++ b/packages/tendermint-rpc/webpack.web.config.js
@@ -16,7 +16,10 @@ module.exports = [
       filename: "tests.js",
     },
     plugins: [
-      new webpack.EnvironmentPlugin({ TENDERMINT_ENABLED: "" }),
+      new webpack.EnvironmentPlugin({
+        HTTPSERVER_ENABLED: "",
+        TENDERMINT_ENABLED: "",
+      }),
       new webpack.ProvidePlugin({
         Buffer: ["buffer", "Buffer"],
       }),