diff --git a/doc/reference/slots.md b/doc/reference/slots.md
index 6f34c2c5..59061fb3 100644
--- a/doc/reference/slots.md
+++ b/doc/reference/slots.md
@@ -37,16 +37,16 @@ rendering context.
 </div>
 ```
 
-Slots are defined by the caller, with the `t-set` directive:
+Slots are defined by the caller, with the `t-set-slot` directive:
 
 ```xml
 <div t-name="SomeComponent">
   <div>some component</div>
   <Dialog title="Some Dialog">
-    <t t-set="content">
+    <t t-set-slot="content">
       <div>hey</div>
     </t>
-    <t t-set="footer">
+    <t t-set-slot="footer">
       <button t-on-click="doSomething">ok</button>
     </t>
   </Dialog>
@@ -57,6 +57,9 @@ In this example, the component `Dialog` will render the slots `content` and `foo
 with its parent as rendering context. This means that clicking on the button
 will execute the `doSomething` method on the parent, not on the dialog.
 
+Note: Owl previously used the `t-set` directive to define the content of a slot.
+This is deprecated and should no longer be used in new code.
+
 ## Reference
 
 Default slot: the first element inside the component which is not a named slot will
diff --git a/roadmap.md b/roadmap.md
index 0d6183e5..d122c610 100644
--- a/roadmap.md
+++ b/roadmap.md
@@ -16,6 +16,8 @@ change!
 
 ### 2.x (2020? 2021? 2022?)
 
+- stop support for `t-set` directive to define the content of a slot
+
 Maybe:
 
 - reimplement vdom to use *block* system, like Vue 3, which should make Owl
diff --git a/src/component/directive.ts b/src/component/directive.ts
index ee1bf14b..8cfbc731 100644
--- a/src/component/directive.ts
+++ b/src/component/directive.ts
@@ -400,7 +400,16 @@ QWeb.addDirective({
 
     if (hasSlots) {
       const clone = <Element>node.cloneNode(true);
-      const slotNodes: Element[] = [];
+      const slotNodes = Array.from(clone.querySelectorAll("[t-set-slot]"));
+
+      // The next code is a fallback for compatibility reason. It accepts t-set
+      // elements that are direct children with a non empty body as nodes defining
+      // the content of a slot.
+      //
+      // This is wrong, but is necessary to prevent breaking all existing Owl
+      // code using slots. This will be removed in v2.0 someday. Meanwhile,
+      // please use t-set-slot everywhere you need to set the content of a
+      // slot.
       for (let el of clone.children) {
         if (el.getAttribute("t-set") && el.hasChildNodes()) {
           slotNodes.push(el);
@@ -412,8 +421,15 @@ QWeb.addDirective({
         for (let i = 0, length = slotNodes.length; i < length; i++) {
           const slotNode = slotNodes[i];
           slotNode.parentElement!.removeChild(slotNode);
-          const key = slotNode.getAttribute("t-set")!;
-          slotNode.removeAttribute("t-set");
+          let key = slotNode.getAttribute("t-set-slot")!;
+          slotNode.removeAttribute("t-set-slot");
+
+          // here again, this code should be removed when we stop supporting
+          // using t-set to define the content of named slots.
+          if (!key) {
+            key = slotNode.getAttribute("t-set")!;
+            slotNode.removeAttribute("t-set");
+          }
           const slotFn = qweb._compile(`slot_${key}_template`, slotNode, ctx);
           QWeb.slots[`${slotId}_${key}`] = slotFn;
         }
diff --git a/tests/component/__snapshots__/slots.test.ts.snap b/tests/component/__snapshots__/slots.test.ts.snap
index 448927e4..ad82605c 100644
--- a/tests/component/__snapshots__/slots.test.ts.snap
+++ b/tests/component/__snapshots__/slots.test.ts.snap
@@ -90,6 +90,96 @@ exports[`t-slot directive can define and call slots 4`] = `
 }"
 `;
 
+exports[`t-slot directive can define and call slots using old t-set keyword 1`] = `
+"function anonymous(context, extra
+) {
+    // Template name: \\"__template__2\\"
+    let utils = this.constructor.utils;
+    let QWeb = this.constructor;
+    let parent = context;
+    let scope = Object.create(context);
+    let h = this.h;
+    let c1 = [], p1 = {key:1};
+    let vn1 = h('div', p1, c1);
+    // Component 'Dialog'
+    let w2 = '__3__' in parent.__owl__.cmap ? parent.__owl__.children[parent.__owl__.cmap['__3__']] : false;
+    let props2 = {};
+    if (w2 && w2.__owl__.currentFiber && !w2.__owl__.vnode) {
+        w2.destroy();
+        w2 = false;
+    }
+    if (w2) {
+        w2.__updateProps(props2, extra.fiber, Object.assign(Object.create(context), scope));
+        let pvnode = w2.__owl__.pvnode;
+        c1.push(pvnode);
+    } else {
+        let componentKey2 = \`Dialog\`;
+        let W2 = context.constructor.components[componentKey2] || QWeb.components[componentKey2]|| scope['Dialog'];
+        if (!W2) {throw new Error('Cannot find the definition of component \\"' + componentKey2 + '\\"')}
+        w2 = new W2(parent, props2);
+        parent.__owl__.cmap['__3__'] = w2.__owl__.id;
+        w2.__owl__.slotId = 1;
+        let fiber = w2.__prepare(extra.fiber, Object.assign(Object.create(context), scope), () => { const vnode = fiber.vnode; pvnode.sel = vnode.sel; });
+        let pvnode = h('dummy', {key: '__3__', hook: {remove() {},destroy(vn) {w2.destroy();}}});
+        c1.push(pvnode);
+        w2.__owl__.pvnode = pvnode;
+    }
+    w2.__owl__.parentLastFiberId = extra.fiber.id;
+    return vn1;
+}"
+`;
+
+exports[`t-slot directive can define and call slots using old t-set keyword 2`] = `
+"function anonymous(context, extra
+) {
+    // Template name: \\"__template__1\\"
+    let h = this.h;
+    let c6 = [], p6 = {key:6};
+    let vn6 = h('div', p6, c6);
+    let c7 = [], p7 = {key:7};
+    let vn7 = h('div', p7, c7);
+    c6.push(vn7);
+    const slot8 = this.constructor.slots[context.__owl__.slotId + '_' + 'header'];
+    if (slot8) {
+        slot8.call(this, context.__owl__.scope, Object.assign({}, extra, {parentNode: c7, parent: extra.parent || context}));
+    }
+    let c9 = [], p9 = {key:9};
+    let vn9 = h('div', p9, c9);
+    c6.push(vn9);
+    const slot10 = this.constructor.slots[context.__owl__.slotId + '_' + 'footer'];
+    if (slot10) {
+        slot10.call(this, context.__owl__.scope, Object.assign({}, extra, {parentNode: c9, parent: extra.parent || context}));
+    }
+    return vn6;
+}"
+`;
+
+exports[`t-slot directive can define and call slots using old t-set keyword 3`] = `
+"function anonymous(context, extra
+) {
+    // Template name: \\"slot_header_template\\"
+    let h = this.h;
+    let c1 = extra.parentNode;
+    let c4 = [], p4 = {key:4};
+    let vn4 = h('span', p4, c4);
+    c1.push(vn4);
+    c4.push({text: \`header\`});
+}"
+`;
+
+exports[`t-slot directive can define and call slots using old t-set keyword 4`] = `
+"function anonymous(context, extra
+) {
+    // Template name: \\"slot_footer_template\\"
+    let h = this.h;
+    let c1 = extra.parentNode;
+    let c5 = [], p5 = {key:5};
+    let vn5 = h('span', p5, c5);
+    c1.push(vn5);
+    c5.push({text: \`footer\`});
+}"
+`;
+
 exports[`t-slot directive content is the default slot 1`] = `
 "function anonymous(context, extra
 ) {
diff --git a/tests/component/slots.test.ts b/tests/component/slots.test.ts
index f43b87bb..7c475807 100644
--- a/tests/component/slots.test.ts
+++ b/tests/component/slots.test.ts
@@ -41,8 +41,8 @@ describe("t-slot directive", () => {
           <templates>
             <div t-name="Parent">
                <Dialog>
-                  <t t-set="header"><span>header</span></t>
-                  <t t-set="footer"><span>footer</span></t>
+                  <t t-set-slot="header"><span>header</span></t>
+                  <t t-set-slot="footer"><span>footer</span></t>
                </Dialog>
             </div>
             <div t-name="Dialog">
@@ -67,6 +67,38 @@ describe("t-slot directive", () => {
     expect(QWeb.slots["1_footer"].toString()).toMatchSnapshot();
   });
 
+  test("can define and call slots using old t-set keyword", async () => {
+    // NOTE: this test should be removed once we stop supporting the t-set directive
+    // for defining slot content.
+    class Dialog extends Component {
+      static template = xml`
+        <div>
+          <div><t t-slot="header"/></div>
+          <div><t t-slot="footer"/></div>
+        </div>`;
+    }
+    class Parent extends Component {
+      static template = xml`
+        <div>
+          <Dialog>
+            <t t-set="header"><span>header</span></t>
+            <t t-set="footer"><span>footer</span></t>
+          </Dialog>
+        </div>`;
+      static components = { Dialog };
+    }
+    const parent = new Parent();
+    await parent.mount(fixture);
+
+    expect(fixture.innerHTML).toBe(
+      "<div><div><div><span>header</span></div><div><span>footer</span></div></div></div>"
+    );
+    expect(env.qweb.templates[Parent.template].fn.toString()).toMatchSnapshot();
+    expect(env.qweb.templates[Dialog.template].fn.toString()).toMatchSnapshot();
+    expect(QWeb.slots["1_header"].toString()).toMatchSnapshot();
+    expect(QWeb.slots["1_footer"].toString()).toMatchSnapshot();
+  });
+
   test("named slots can define a default content", async () => {
     class Dialog extends Component {
       static template = xml`
@@ -128,7 +160,7 @@ describe("t-slot directive", () => {
           </span>`;
     }
     class Parent extends Component {
-      static template = xml`<div><Dialog><t t-set="header">hey</t></Dialog></div>`;
+      static template = xml`<div><Dialog><t t-set-slot="header">hey</t></Dialog></div>`;
       static components = { Dialog };
     }
     const parent = new Parent();
@@ -143,7 +175,7 @@ describe("t-slot directive", () => {
             <div t-name="Parent">
               <span class="counter"><t t-esc="state.val"/></span>
               <Dialog>
-                <t t-set="footer"><button t-on-click="doSomething">do something</button></t>
+                <t t-set-slot="footer"><button t-on-click="doSomething">do something</button></t>
               </Dialog>
             </div>
             <span t-name="Dialog"><t t-slot="footer"/></span>
@@ -302,7 +334,7 @@ describe("t-slot directive", () => {
             <div>
               <span class="counter"><t t-esc="state.val"/></span>
               <Dialog>
-                <t t-set="footer"><button t-ref="myButton" t-on-click="doSomething">do something</button></t>
+                <t t-set-slot="footer"><button t-ref="myButton" t-on-click="doSomething">do something</button></t>
               </Dialog>
             </div>
           `;
@@ -376,7 +408,7 @@ describe("t-slot directive", () => {
           <templates>
             <div t-name="Parent">
                <Dialog>
-                  <t t-set="content">
+                  <t t-set-slot="content">
                       <span>sts</span>
                       <span>rocks</span>
                   </t>
@@ -442,14 +474,14 @@ describe("t-slot directive", () => {
     expect(fixture.innerHTML).toBe("<div><span><span>some content</span></span></div>");
   });
 
-  test("t-debug on a t-set (defining a slot)", async () => {
+  test("t-debug on a t-set-slot (defining a slot)", async () => {
     const consoleLog = console.log;
     console.log = jest.fn();
 
     env.qweb.addTemplates(`
           <templates>
             <div t-name="Parent">
-              <Dialog><t t-set="content" t-debug="">abc</t></Dialog>
+              <Dialog><t t-set-slot="content" t-debug="">abc</t></Dialog>
             </div>
             <span t-name="Dialog">
               <t t-slot="content"/>
@@ -623,8 +655,8 @@ describe("t-slot directive", () => {
     class A extends Component {
       static template = xml`
           <B>
-            <t t-set="s1"><C val="1"/></t>
-            <t t-set="s2"><C val="2"/></t>
+            <t t-set-slot="s1"><C val="1"/></t>
+            <t t-set-slot="s2"><C val="2"/></t>
           </B>`;
       static components = { B, C };
     }
diff --git a/tools/playground/samples.js b/tools/playground/samples.js
index e0e3635e..0423f140 100644
--- a/tools/playground/samples.js
+++ b/tools/playground/samples.js
@@ -1169,7 +1169,7 @@ const RESPONSIVE_CSS = `body {
 const SLOTS = `// We show here how slots can be used to create generic components.
 // In this example, the Card component is basically only a container. It is not
 // aware of its content. It just knows where it should be (with t-slot).
-// The parent component define the content with t-set.
+// The parent component define the content with t-set-slot.
 //
 // Note that the t-on-click event, defined in the App template, is executed in
 // the context of the App component, even though it is inside the Card component
@@ -1235,15 +1235,15 @@ const SLOTS_XML = `<templates>
 
   <div t-name="App" class="main">
     <Card title="'Title card A'">
-      <t t-set="content">Content of card 1...  [<t t-esc="state.a"/>]</t>
-      <t t-set="footer"><button t-on-click="inc('a', 1)">Increment A</button></t>
+      <t t-set-slot="content">Content of card 1...  [<t t-esc="state.a"/>]</t>
+      <t t-set-slot="footer"><button t-on-click="inc('a', 1)">Increment A</button></t>
     </Card>
     <Card title="'Title card B'">
-      <t t-set="content">
+      <t t-set-slot="content">
         <div>Card 2... [<t t-esc="state.b"/>]</div>
         <Counter />
       </t>
-      <t t-set="footer"><button t-on-click="inc('b', -1)">Decrement B</button></t>
+      <t t-set-slot="footer"><button t-on-click="inc('b', -1)">Decrement B</button></t>
     </Card>
   </div>
 </templates>`;