diff --git a/browser/ui/views/frame/vertical_tab_strip_region_view.cc b/browser/ui/views/frame/vertical_tab_strip_region_view.cc
index 1a933b6da65d..f57b891bac82 100644
--- a/browser/ui/views/frame/vertical_tab_strip_region_view.cc
+++ b/browser/ui/views/frame/vertical_tab_strip_region_view.cc
@@ -685,9 +685,19 @@ void VerticalTabStripRegionView::OnWidgetDestroying(views::Widget* widget) {
   widget_observation_.Reset();
 }
 
-bool VerticalTabStripRegionView::IsFullscreen() const {
-  auto* widget = GetWidget();
-  return widget && widget->GetTopLevelWidget()->IsFullscreen();
+bool VerticalTabStripRegionView::IsTabFullscreen() const {
+  auto* exclusive_access_manager = browser_->exclusive_access_manager();
+  if (!exclusive_access_manager) {
+    return false;
+  }
+
+  auto* fullscreen_controller =
+      exclusive_access_manager->fullscreen_controller();
+  if (!fullscreen_controller) {
+    return false;
+  }
+
+  return fullscreen_controller->IsWindowFullscreenForTabOrPending();
 }
 
 void VerticalTabStripRegionView::SetState(State state) {
@@ -1080,7 +1090,7 @@ gfx::Size VerticalTabStripRegionView::GetPreferredSizeForState(
     return {};
   }
 
-  if (IsFullscreen()) {
+  if (IsTabFullscreen()) {
     return {};
   }
 
diff --git a/browser/ui/views/frame/vertical_tab_strip_region_view.h b/browser/ui/views/frame/vertical_tab_strip_region_view.h
index 79739c83d114..8240b68cbd45 100644
--- a/browser/ui/views/frame/vertical_tab_strip_region_view.h
+++ b/browser/ui/views/frame/vertical_tab_strip_region_view.h
@@ -19,7 +19,7 @@
 
 namespace views {
 class ResizeArea;
-}  // namespace views
+}
 
 class BraveNewTabButton;
 class BrowserView;
@@ -116,7 +116,7 @@ class VerticalTabStripRegionView : public views::View,
   FRIEND_TEST_ALL_PREFIXES(VerticalTabStripBrowserTest,
                            OriginalTabSearchButton);
 
-  bool IsFullscreen() const;
+  bool IsTabFullscreen() const;
 
   void SetState(State state);
 
diff --git a/browser/ui/views/tabs/vertical_tab_strip_browsertest.cc b/browser/ui/views/tabs/vertical_tab_strip_browsertest.cc
index a3493b76b467..a7bad5eaf073 100644
--- a/browser/ui/views/tabs/vertical_tab_strip_browsertest.cc
+++ b/browser/ui/views/tabs/vertical_tab_strip_browsertest.cc
@@ -391,31 +391,12 @@ IN_PROC_BROWSER_TEST_F(VerticalTabStripBrowserTest, MAYBE_Fullscreen) {
     observer.Wait();
   }
 
-  base::RunLoop run_loop;
-  auto wait_until = base::BindLambdaForTesting(
-      [&](base::RepeatingCallback<bool()> predicate) {
-        if (predicate.Run()) {
-          return;
-        }
-
-        base::RepeatingTimer scheduler;
-        scheduler.Start(FROM_HERE, base::Milliseconds(100),
-                        base::BindLambdaForTesting([&]() {
-                          if (predicate.Run()) {
-                            run_loop.Quit();
-                          }
-                        }));
-        run_loop.Run();
-      });
-
-  // Vertical tab strip should be invisible on browser fullscreen.
+  // Vertical tab strip should be visible on browser fullscreen.
   ASSERT_TRUE(fullscreen_controller->IsFullscreenForBrowser());
   ASSERT_TRUE(browser_view()->IsFullscreen());
-  wait_until.Run(base::BindLambdaForTesting([&]() {
-    return !browser_view()
-                ->vertical_tab_strip_host_view_->GetPreferredSize()
-                .width();
-  }));
+  EXPECT_TRUE(browser_view()
+                  ->vertical_tab_strip_host_view_->GetPreferredSize()
+                  .width());
 
   {
     auto observer = FullscreenNotificationObserver(browser());
@@ -427,6 +408,7 @@ IN_PROC_BROWSER_TEST_F(VerticalTabStripBrowserTest, MAYBE_Fullscreen) {
 
   {
     auto observer = FullscreenNotificationObserver(browser());
+    // Vertical tab strip should become invisible on tab fullscreen.
     fullscreen_controller->EnterFullscreenModeForTab(
         browser_view()
             ->browser()
@@ -436,8 +418,6 @@ IN_PROC_BROWSER_TEST_F(VerticalTabStripBrowserTest, MAYBE_Fullscreen) {
 
     observer.Wait();
   }
-
-  // Vertical tab strip should be invisible on tab fullscreen.
   ASSERT_TRUE(fullscreen_controller->IsTabFullscreen());
   if (!browser_view()
            ->vertical_tab_strip_host_view_->GetPreferredSize()
@@ -445,6 +425,28 @@ IN_PROC_BROWSER_TEST_F(VerticalTabStripBrowserTest, MAYBE_Fullscreen) {
     return;
   }
 
+  base::RunLoop run_loop;
+  auto wait_until = base::BindLambdaForTesting(
+      [&](base::RepeatingCallback<bool()> predicate) {
+        if (predicate.Run()) {
+          return;
+        }
+
+        base::RepeatingTimer scheduler;
+        scheduler.Start(FROM_HERE, base::Milliseconds(100),
+                        base::BindLambdaForTesting([&]() {
+                          if (predicate.Run()) {
+                            run_loop.Quit();
+                          } else {
+                            LOG(ERROR) << browser_view()
+                                              ->vertical_tab_strip_host_view_
+                                              ->GetPreferredSize()
+                                              .width();
+                          }
+                        }));
+        run_loop.Run();
+      });
+
   wait_until.Run(base::BindLambdaForTesting([&]() {
     return !browser_view()
                 ->vertical_tab_strip_host_view_->GetPreferredSize()