diff --git a/packages/@headlessui-react/src/components/tabs/tabs.test.tsx b/packages/@headlessui-react/src/components/tabs/tabs.test.tsx
index 310f847..3292579 100644
--- a/packages/@headlessui-react/src/components/tabs/tabs.test.tsx
+++ b/packages/@headlessui-react/src/components/tabs/tabs.test.tsx
@@ -804,6 +804,145 @@ describe('Rendering', () => {
         assertTabs({ active: 2 })
       })
     )
+
+    it(
+      'should select first tab if no tabs were provided originally',
+      suppressConsoleLogs(async () => {
+        function Example({ defaultIndex = undefined }: { defaultIndex?: number } = {}) {
+          let [tabs, setTabs] = useState<string[]>([])
+
+          return (
+            <>
+              <Tab.Group defaultIndex={defaultIndex}>
+                <Tab.List>
+                  {tabs.map((tab, index) => (
+                    <Tab key={index}>{tab}</Tab>
+                  ))}
+                </Tab.List>
+                <Tab.Panels>
+                  {tabs.map((tab, index) => (
+                    <Tab.Panel key={index}>content: {tab}</Tab.Panel>
+                  ))}
+                </Tab.Panels>
+              </Tab.Group>
+
+              <button onClick={() => setTabs(['tab 1', 'tab 2', 'tab 3'])}>change</button>
+            </>
+          )
+        }
+
+        render(<Example defaultIndex={0} />)
+
+        assertActiveElement(document.body)
+
+        // There are no tab initially
+        assertTabs({ active: -1 })
+
+        // There are not tabs so this should not change anything
+        await press(Keys.Tab)
+        assertTabs({ active: -1 })
+
+        // Add some tabs
+        await click(getByText('change'))
+
+        // When going from no tabs to some tabs, the tab based on defaultIndex should be selected
+        assertTabs({ active: 0 })
+      })
+    )
+
+    it(
+      'should select first tab if no tabs were provided originally (with a defaultIndex of 1)',
+      suppressConsoleLogs(async () => {
+        function Example({ defaultIndex = undefined }: { defaultIndex?: number } = {}) {
+          let [tabs, setTabs] = useState<string[]>([])
+
+          return (
+            <>
+              <Tab.Group defaultIndex={defaultIndex}>
+                <Tab.List>
+                  {tabs.map((tab, index) => (
+                    <Tab key={index}>{tab}</Tab>
+                  ))}
+                </Tab.List>
+                <Tab.Panels>
+                  {tabs.map((tab, index) => (
+                    <Tab.Panel key={index}>content: {tab}</Tab.Panel>
+                  ))}
+                </Tab.Panels>
+              </Tab.Group>
+
+              <button onClick={() => setTabs(['tab 1', 'tab 2', 'tab 3'])}>change</button>
+            </>
+          )
+        }
+
+        render(<Example defaultIndex={1} />)
+
+        assertActiveElement(document.body)
+
+        // There are no tab initially
+        assertTabs({ active: -1 })
+
+        // There are not tabs so this should not change anything
+        await press(Keys.Tab)
+        assertTabs({ active: -1 })
+
+        // Add some tabs
+        await click(getByText('change'))
+
+        // When going from no tabs to some tabs, the tab based on defaultIndex should be selected
+        assertTabs({ active: 1 })
+      })
+    )
+
+    it(
+      'should select first tab if no tabs were provided originally (with a defaultIndex of 1)',
+      suppressConsoleLogs(async () => {
+        function Example({ defaultIndex = undefined }: { defaultIndex?: number } = {}) {
+          let [tabs, setTabs] = useState<string[]>([])
+
+          return (
+            <>
+              <Tab.Group defaultIndex={defaultIndex}>
+                <Tab.List>
+                  {tabs.map((tab, index) => (
+                    <Tab key={index}>{tab}</Tab>
+                  ))}
+                </Tab.List>
+                <Tab.Panels>
+                  {tabs.map((tab, index) => (
+                    <Tab.Panel key={index}>content: {tab}</Tab.Panel>
+                  ))}
+                </Tab.Panels>
+              </Tab.Group>
+
+              <button onClick={() => setTabs(['tab 1', 'tab 2', 'tab 3'])}>change 1</button>
+              <button onClick={() => setTabs([])}>change 2</button>
+              <button onClick={() => setTabs(['tab 1', 'tab 2', 'tab 3'])}>change 3</button>
+            </>
+          )
+        }
+
+        render(<Example defaultIndex={1} />)
+
+        assertActiveElement(document.body)
+
+        // There are no tab initially
+        assertTabs({ active: -1 })
+
+        // There are not tabs so this should not change anything
+        await press(Keys.Tab)
+        assertTabs({ active: -1 })
+
+        // Add some tabs
+        await click(getByText('change 1'))
+        await click(getByText('change 2'))
+        await click(getByText('change 3'))
+
+        // When going from no tabs to some tabs, the tab based on defaultIndex should be selected
+        assertTabs({ active: 1 })
+      })
+    )
   })
 
   describe('`selectedIndex`', () => {
diff --git a/packages/@headlessui-react/src/components/tabs/tabs.tsx b/packages/@headlessui-react/src/components/tabs/tabs.tsx
index 4a633b5..748ccd1 100644
--- a/packages/@headlessui-react/src/components/tabs/tabs.tsx
+++ b/packages/@headlessui-react/src/components/tabs/tabs.tsx
@@ -99,6 +99,15 @@ let reducers: {
         [Ordering.Greater]: () => Direction.Forwards,
       })
 
+      // If there are no focusable tabs then.
+      // We won't change the selected index
+      // because it's likely the user is
+      // lazy loading tabs and there's
+      // nothing to focus on yet
+      if (focusableTabs.length === 0) {
+        return nextState
+      }
+
       return {
         ...nextState,
         selectedIndex: match(direction, {
diff --git a/packages/@headlessui-vue/src/components/tabs/tabs.test.ts b/packages/@headlessui-vue/src/components/tabs/tabs.test.ts
index 64d7104..638a367 100644
--- a/packages/@headlessui-vue/src/components/tabs/tabs.test.ts
+++ b/packages/@headlessui-vue/src/components/tabs/tabs.test.ts
@@ -721,6 +721,140 @@ describe('Rendering', () => {
       // Nothing should change...
       assertTabs({ active: 2 })
     })
+
+    it(
+      'should select first tab if no tabs were provided originally',
+      suppressConsoleLogs(async () => {
+        renderTemplate({
+          template: html`
+            <TabGroup :defaultIndex="0">
+              <TabList>
+                <Tab v-for="tab in tabs">{{ tab }}</Tab>
+              </TabList>
+              <TabPanels>
+                <TabPanel v-for="tab in tabs">content for: {{ tab }}</TabPanel>
+              </TabPanels>
+            </TabGroup>
+
+            <button>after</button>
+            <button @click="tabs.value = ['tab 1', 'tab 2', 'tab 3']">change</button>
+          `,
+          setup() {
+            let tabs = ref<string[]>([])
+            return {
+              tabs,
+            }
+          },
+        })
+
+        assertActiveElement(document.body)
+
+        // There are no tab initially
+        assertTabs({ active: -1 })
+
+        // There are not tabs so this should not change anything
+        await press(Keys.Tab)
+        assertTabs({ active: -1 })
+
+        // Add some tabs
+        await click(getByText('change'))
+
+        // When going from no tabs to some tabs, the tab based on defaultIndex should be selected
+        assertTabs({ active: 0 })
+      })
+    )
+
+    it(
+      'should select first tab if no tabs were provided originally (with a defaultIndex of 1)',
+      suppressConsoleLogs(async () => {
+        renderTemplate({
+          template: html`
+            <TabGroup :defaultIndex="1">
+              <TabList>
+                <Tab v-for="tab in tabs">{{ tab }}</Tab>
+              </TabList>
+              <TabPanels>
+                <TabPanel v-for="tab in tabs">content for: {{ tab }}</TabPanel>
+              </TabPanels>
+            </TabGroup>
+
+            <button>after</button>
+            <button @click="tabs.value = ['tab 1', 'tab 2', 'tab 3']">change</button>
+          `,
+          setup() {
+            let tabs = ref<string[]>([])
+            return {
+              tabs,
+            }
+          },
+        })
+
+        assertActiveElement(document.body)
+
+        // There are no tab initially
+        assertTabs({ active: -1 })
+
+        // There are not tabs so this should not change anything
+        await press(Keys.Tab)
+        assertTabs({ active: -1 })
+
+        // Add some tabs
+        await click(getByText('change'))
+
+        // When going from no tabs to some tabs, the tab based on defaultIndex should be selected
+        assertTabs({ active: 1 })
+      })
+    )
+
+    it(
+      'should select first tab if no tabs were provided originally (with a defaultIndex of 1)',
+      suppressConsoleLogs(async () => {
+        renderTemplate({
+          template: html`
+            <TabGroup :defaultIndex="1">
+              <TabList>
+                <Tab v-for="tab in tabs">{{ tab }}</Tab>
+              </TabList>
+              <TabPanels>
+                <TabPanel v-for="tab in tabs">content for: {{ tab }}</TabPanel>
+              </TabPanels>
+            </TabGroup>
+
+            <button>after</button>
+            <button @click="tabs.value = ['tab 1', 'tab 2', 'tab 3']">change 1</button>
+            <button @click="tabs.value = []">change 2</button>
+            <button @click="tabs.value = ['tab 1', 'tab 2', 'tab 3']">change 3</button>
+          `,
+          setup() {
+            let tabs = ref<string[]>([])
+            return {
+              tabs,
+            }
+          },
+        })
+
+        assertActiveElement(document.body)
+
+        // There are no tab initially
+        assertTabs({ active: -1 })
+
+        // There are not tabs so this should not change anything
+        await press(Keys.Tab)
+        assertTabs({ active: -1 })
+
+        // Add some tabs
+        await click(getByText('change 1'))
+
+        // Add some tabs
+        await click(getByText('change 2'))
+
+        // Add some tabs
+        await click(getByText('change 3'))
+
+        // When going from no tabs to some tabs, the tab based on defaultIndex should be selected
+        assertTabs({ active: 1 })
+      })
+    )
   })
 })