diff --git a/addons/mail/static/src/core/common/chat_window_service.js b/addons/mail/static/src/core/common/chat_window_service.js
index 5067cb16288..f4772205f73 100644
--- a/addons/mail/static/src/core/common/chat_window_service.js
+++ b/addons/mail/static/src/core/common/chat_window_service.js
@@ -68,8 +68,9 @@ export class ChatWindowService {
             : CHAT_WINDOW_END_GAP_WIDTH;
         const endGap = this.ui.isSmall ? 0 : CHAT_WINDOW_END_GAP_WIDTH;
         const available = browser.innerWidth - startGap - endGap;
-        const maxAmountWithoutHidden = Math.floor(
-            available / (CHAT_WINDOW_WIDTH + CHAT_WINDOW_INBETWEEN_WIDTH)
+        const maxAmountWithoutHidden = Math.max(
+            1,
+            Math.floor(available / (CHAT_WINDOW_WIDTH + CHAT_WINDOW_INBETWEEN_WIDTH))
         );
         return maxAmountWithoutHidden;
     }
diff --git a/addons/mail/static/tests/chat_window/chat_window_tests.js b/addons/mail/static/tests/chat_window/chat_window_tests.js
index 27b161cb45b..936998bf1d0 100644
--- a/addons/mail/static/tests/chat_window/chat_window_tests.js
+++ b/addons/mail/static/tests/chat_window/chat_window_tests.js
@@ -236,6 +236,17 @@ QUnit.test("chat window: open / close", async (assert) => {
     assert.verifySteps(["rpc:channel_fold/open"]);
 });
 
+QUnit.test("open chat on very narrow device should work", async (assert) => {
+    const pyEnv = await startServer();
+    patchUiSize({ width: 200 });
+    pyEnv["discuss.channel"].create({});
+    await start();
+    assert.ok(CHAT_WINDOW_WIDTH > 200, "Device is narrower than usual chat window width"); // scenario where this might fail
+    await click("button i[aria-label='Messages']");
+    await click(".o-mail-NotificationItem");
+    assert.containsOnce($, ".o-mail-ChatWindow");
+});
+
 QUnit.test(
     "Mobile: closing a chat window should not update channel state on the server",
     async (assert) => {