diff --git a/packages/binding-mqtt/src/mqtt-client.ts b/packages/binding-mqtt/src/mqtt-client.ts
index 9fc120155..4eba3ac30 100644
--- a/packages/binding-mqtt/src/mqtt-client.ts
+++ b/packages/binding-mqtt/src/mqtt-client.ts
@@ -65,7 +65,10 @@ export default class MqttClient implements ProtocolClient {
         const brokerUri: string = `${this.scheme}://` + requestUri.host;
         // Keeping the path as the topic for compatibility reasons.
         // Current specification allows only form["mqv:filter"]
-        const filter = requestUri.pathname.slice(1) ?? form["mqv:filter"];
+        const filter = requestUri.pathname.slice(1) || form["mqv:filter"];
+        if (filter == null) {
+            throw new Error("MqttClient: no filter found in form href or mqv:filter");
+        }
 
         let pool = this.pools.get(brokerUri);
 
@@ -95,7 +98,10 @@ export default class MqttClient implements ProtocolClient {
         const brokerUri: string = `${this.scheme}://` + requestUri.host;
         // Keeping the path as the topic for compatibility reasons.
         // Current specification allows only form["mqv:filter"]
-        const filter = requestUri.pathname.slice(1) ?? form["mqv:filter"];
+        const filter = requestUri.pathname.slice(1) || form["mqv:filter"];
+        if (filter == null) {
+            throw new Error("MqttClient: no filter found in form href or mqv:filter");
+        }
 
         let pool = this.pools.get(brokerUri);
 
@@ -125,7 +131,10 @@ export default class MqttClient implements ProtocolClient {
     public async writeResource(form: MqttForm, content: Content): Promise<void> {
         const requestUri = new url.URL(form.href);
         const brokerUri = `${this.scheme}://${requestUri.host}`;
-        const topic = requestUri.pathname.slice(1) ?? form["mqv:topic"];
+        const topic = requestUri.pathname.slice(1) || form["mqv:topic"];
+        if (topic == null) {
+            throw new Error("MqttClient: no topic found in form href or mqv:topic");
+        }
 
         let pool = this.pools.get(brokerUri);
 
@@ -146,9 +155,13 @@ export default class MqttClient implements ProtocolClient {
 
     public async invokeResource(form: MqttForm, content: Content): Promise<Content> {
         const requestUri = new url.URL(form.href);
-        const topic = requestUri.pathname.slice(1);
+        const topic = requestUri.pathname.slice(1) || form["mqv:topic"];
         const brokerUri = `${this.scheme}://${requestUri.host}`;
 
+        if (topic == null) {
+            throw new Error("MqttClient: no topic found in form href or mqv:topic");
+        }
+
         let pool = this.pools.get(brokerUri);
 
         if (pool == null) {
diff --git a/packages/binding-mqtt/test/mqtt-client-form-test.unit.ts b/packages/binding-mqtt/test/mqtt-client-form-test.unit.ts
new file mode 100644
index 000000000..61a98e814
--- /dev/null
+++ b/packages/binding-mqtt/test/mqtt-client-form-test.unit.ts
@@ -0,0 +1,74 @@
+/********************************************************************************
+ * Copyright (c) 2026 Contributors to the Eclipse Foundation
+ *
+ * See the NOTICE file(s) distributed with this work for additional
+ * information regarding copyright ownership.
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Public License v. 2.0 which is available at
+ * http://www.eclipse.org/legal/epl-2.0, or the W3C Software Notice and
+ * Document License (2015-05-13) which is available at
+ * https://www.w3.org/Consortium/Legal/2015/copyright-software-and-document.
+ *
+ * SPDX-License-Identifier: EPL-2.0 OR W3C-20150513
+ ********************************************************************************/
+
+import { expect } from "chai";
+import sinon from "sinon";
+import { MqttClient } from "../src/mqtt";
+import MQTTMessagePool from "../src/mqtt-message-pool";
+import { Readable } from "stream";
+import { Content } from "@node-wot/core";
+
+describe("MQTT client form parsing - unit", () => {
+    let subscribe: sinon.SinonStub;
+    let publish: sinon.SinonStub;
+
+    beforeEach(() => {
+        sinon.stub(MQTTMessagePool.prototype, "connect").resolves();
+        subscribe = sinon.stub(MQTTMessagePool.prototype, "subscribe").resolves();
+        publish = sinon.stub(MQTTMessagePool.prototype, "publish").resolves();
+        sinon.stub(MQTTMessagePool.prototype, "unsubscribe").resolves();
+    });
+
+    afterEach(() => {
+        sinon.restore();
+    });
+
+    it("should fall back to mqv:filter when href has no path in subscribe", async () => {
+        await new MqttClient().subscribeResource({ href: "mqtt://localhost:1883", "mqv:filter": "foo/bar" }, () => {});
+
+        expect(subscribe.firstCall.args[0]).to.equal("foo/bar");
+    });
+
+    it("should fall back to mqv:filter when href has no path in read property", async () => {
+        // readResource resolves only once a message arrives on the subscription
+        subscribe.callsFake(async (filter: string, onMessage: (topic: string, message: Buffer) => void) =>
+            onMessage(filter, Buffer.from("42"))
+        );
+
+        await new MqttClient().readResource({ href: "mqtt://localhost:1883", "mqv:filter": "foo/bar" });
+
+        expect(subscribe.firstCall.args[0]).to.equal("foo/bar");
+    });
+
+    it("should fall back to mqv:topic when href has no path in write property", async () => {
+        const stream = Readable.from(Buffer.from("23"));
+        await new MqttClient().writeResource(
+            { href: "mqtt://localhost:1883", "mqv:topic": "foo/bar" },
+            new Content("application/json", stream)
+        );
+
+        expect(publish.firstCall.args[0]).to.equal("foo/bar");
+    });
+
+    it("should fall back to mqv:topic when href has no path in invoke action", async () => {
+        const stream = Readable.from(Buffer.from("23"));
+        await new MqttClient().invokeResource(
+            { href: "mqtt://localhost:1883", "mqv:topic": "foo/bar" },
+            new Content("application/json", stream)
+        );
+
+        expect(publish.firstCall.args[0]).to.equal("foo/bar");
+    });
+});