diff --git a/CHANGELOG.md b/CHANGELOG.md
index 0ef77990d1..e5ffa476af 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,6 +6,12 @@ and this project adheres to
 
 ## [Unreleased]
 
+### Changed
+
+- @cosmjs/tendermint-rpc: Require protocol to be set in endpoint URLs (https://,
+  http://, wss:// or ws://). Otherwise an error is raised instead of falling
+  back to ws://.
+
 ## [0.32.1] - 2023-12-04
 
 ### Fixed
diff --git a/packages/tendermint-rpc/src/rpcclients/httpbatchclient.ts b/packages/tendermint-rpc/src/rpcclients/httpbatchclient.ts
index 4b8e4fe653..8d2267a02d 100644
--- a/packages/tendermint-rpc/src/rpcclients/httpbatchclient.ts
+++ b/packages/tendermint-rpc/src/rpcclients/httpbatchclient.ts
@@ -42,8 +42,10 @@ export class HttpBatchClient implements RpcClient {
       dispatchInterval: options.dispatchInterval ?? defaultHttpBatchClientOptions.dispatchInterval,
     };
     if (typeof endpoint === "string") {
-      // accept host.name:port and assume http protocol
-      this.url = hasProtocol(endpoint) ? endpoint : "http://" + endpoint;
+      if (!hasProtocol(endpoint)) {
+        throw new Error("Endpoint URL is missing a protocol. Expected 'https://' or 'http://'.");
+      }
+      this.url = endpoint;
     } else {
       this.url = endpoint.url;
       this.headers = endpoint.headers;
diff --git a/packages/tendermint-rpc/src/rpcclients/httpclient.ts b/packages/tendermint-rpc/src/rpcclients/httpclient.ts
index a17e9699e3..b4107b321b 100644
--- a/packages/tendermint-rpc/src/rpcclients/httpclient.ts
+++ b/packages/tendermint-rpc/src/rpcclients/httpclient.ts
@@ -28,8 +28,10 @@ export class HttpClient implements RpcClient {
 
   public constructor(endpoint: string | HttpEndpoint) {
     if (typeof endpoint === "string") {
-      // accept host.name:port and assume http protocol
-      this.url = hasProtocol(endpoint) ? endpoint : "http://" + endpoint;
+      if (!hasProtocol(endpoint)) {
+        throw new Error("Endpoint URL is missing a protocol. Expected 'https://' or 'http://'.");
+      }
+      this.url = endpoint;
     } else {
       this.url = endpoint.url;
       this.headers = endpoint.headers;
diff --git a/packages/tendermint-rpc/src/rpcclients/rpcclient.spec.ts b/packages/tendermint-rpc/src/rpcclients/rpcclient.spec.ts
index a5fb0310bd..ce27f62751 100644
--- a/packages/tendermint-rpc/src/rpcclients/rpcclient.spec.ts
+++ b/packages/tendermint-rpc/src/rpcclients/rpcclient.spec.ts
@@ -1,7 +1,7 @@
 import { createJsonRpcRequest } from "../jsonrpc";
 import { defaultInstance } from "../testutil.spec";
 import { HttpClient } from "./httpclient";
-import { instanceOfRpcStreamingClient } from "./rpcclient";
+import { hasProtocol, instanceOfRpcStreamingClient } from "./rpcclient";
 import { WebsocketClient } from "./websocketclient";
 
 function pendingWithoutTendermint(): void {
@@ -41,3 +41,30 @@ describe("RpcClient", () => {
     wsClient.disconnect();
   });
 });
+
+describe("hasProtocol", () => {
+  it("works", () => {
+    expect(hasProtocol("https://my.rpc.net")).toEqual(true);
+    expect(hasProtocol("https://my.rpc.net:443")).toEqual(true);
+    expect(hasProtocol("https://my.rpc.net:443/somewhere")).toEqual(true);
+    expect(hasProtocol("http://my.rpc.net")).toEqual(true);
+    expect(hasProtocol("http://my.rpc.net:443")).toEqual(true);
+    expect(hasProtocol("http://my.rpc.net:443/somewhere")).toEqual(true);
+    expect(hasProtocol("wss://my.rpc.net")).toEqual(true);
+    expect(hasProtocol("wss://my.rpc.net:443")).toEqual(true);
+    expect(hasProtocol("wss://my.rpc.net:443/somewhere")).toEqual(true);
+    expect(hasProtocol("ws://my.rpc.net")).toEqual(true);
+    expect(hasProtocol("ws://my.rpc.net:443")).toEqual(true);
+    expect(hasProtocol("ws://my.rpc.net:443/somewhere")).toEqual(true);
+    expect(hasProtocol("ws://my.rpc.net:443/somewhere")).toEqual(true);
+    expect(hasProtocol("file:///Users/joe/Library/CloudStorage/Notes.pdf")).toEqual(true);
+
+    // Protocols without double slash is not what we want to see here
+    expect(hasProtocol("tel:+1-201-555-0123")).toEqual(false);
+
+    // No protocols
+    expect(hasProtocol("")).toEqual(false);
+    expect(hasProtocol(" ")).toEqual(false);
+    expect(hasProtocol("/")).toEqual(false);
+  });
+});
diff --git a/packages/tendermint-rpc/src/rpcclients/websocketclient.ts b/packages/tendermint-rpc/src/rpcclients/websocketclient.ts
index d5485b3536..52803d1b62 100644
--- a/packages/tendermint-rpc/src/rpcclients/websocketclient.ts
+++ b/packages/tendermint-rpc/src/rpcclients/websocketclient.ts
@@ -143,11 +143,13 @@ export class WebsocketClient implements RpcStreamingClient {
   private readonly subscriptionStreams = new Map<string, Stream<SubscriptionEvent>>();
 
   public constructor(baseUrl: string, onError: (err: any) => void = defaultErrorHandler) {
-    // accept host.name:port and assume ws protocol
+    if (!hasProtocol(baseUrl)) {
+      throw new Error("Base URL is missing a protocol. Expected 'ws://' or 'wss://'.");
+    }
+
     // make sure we don't end up with ...//websocket
     const path = baseUrl.endsWith("/") ? "websocket" : "/websocket";
-    const cleanBaseUrl = hasProtocol(baseUrl) ? baseUrl : "ws://" + baseUrl;
-    this.url = cleanBaseUrl + path;
+    this.url = baseUrl + path;
 
     this.socket = new ReconnectingSocket(this.url);