diff --git a/widget/gtk/nsWindow.cpp b/widget/gtk/nsWindow.cpp
index 4d88b24e5fff..1bf159d6348a 100644
--- a/widget/gtk/nsWindow.cpp
+++ b/widget/gtk/nsWindow.cpp
@@ -390,7 +390,8 @@ static void GtkWindowSetTransientFor(GtkWindow* aWindow, GtkWindow* aParent) {
   }
 
 nsWindow::nsWindow()
-    : mDestroyMutex("nsWindow::mDestroyMutex"),
+    : mTitlebarRectMutex("nsWindow::mTitlebarRectMutex"),
+      mDestroyMutex("nsWindow::mDestroyMutex"),
       mIsDestroyed(false),
       mIsShown(false),
       mNeedsShow(false),
@@ -5360,6 +5361,8 @@ void nsWindow::OnWindowStateEvent(GtkWidget* aWidget,
     } else {
       ClearTransparencyBitmap();
     }
+  } else {
+    SetTitlebarRect();
   }
 }
 
@@ -7040,6 +7043,8 @@ void nsWindow::UpdateTopLevelOpaqueRegion() {
     moz_container_wayland_update_opaque_region(mContainer, radius);
   }
 #endif
+
+  SetTitlebarRect();
 }
 
 bool nsWindow::IsChromeWindowTitlebar() {
@@ -7215,22 +7220,20 @@ nsresult nsWindow::UpdateTranslucentWindowAlphaInternal(const nsIntRect& aRect,
 
 #define TITLEBAR_HEIGHT 10
 
-LayoutDeviceIntRect nsWindow::GetTitlebarRect() {
-  // See NS_NATIVE_EGL_WINDOW why we can't block here.
-  auto ret = LayoutDeviceIntRect();
+void nsWindow::SetTitlebarRect() {
+  MutexAutoLock lock(mTitlebarRectMutex);
 
-  if (mDestroyMutex.TryLock()) {
-    if (mGdkWindow && mDrawInTitlebar) {
-      int height = 0;
-      if (DoDrawTilebarCorners()) {
-        height = GdkCeiledScaleFactor() * TITLEBAR_HEIGHT;
-      }
-      ret = LayoutDeviceIntRect(0, 0, mBounds.width, height);
-    }
-    mDestroyMutex.Unlock();
+  if (!mGdkWindow || !DoDrawTilebarCorners()) {
+    mTitlebarRect = LayoutDeviceIntRect();
+    return;
   }
+  mTitlebarRect = LayoutDeviceIntRect(0, 0, mBounds.width,
+                                      GdkCeiledScaleFactor() * TITLEBAR_HEIGHT);
+}
 
-  return ret;
+LayoutDeviceIntRect nsWindow::GetTitlebarRect() {
+  MutexAutoLock lock(mTitlebarRectMutex);
+  return mTitlebarRect;
 }
 
 void nsWindow::UpdateTitlebarTransparencyBitmap() {
@@ -9018,6 +9021,8 @@ void nsWindow::SetDrawsInTitlebar(bool aState) {
     } else {
       ClearTransparencyBitmap();
     }
+  } else {
+    SetTitlebarRect();
   }
 }
 
diff --git a/widget/gtk/nsWindow.h b/widget/gtk/nsWindow.h
index 183b4a9e7ebf..e235d12c0837 100644
--- a/widget/gtk/nsWindow.h
+++ b/widget/gtk/nsWindow.h
@@ -367,6 +367,7 @@ class nsWindow final : public nsBaseWidget {
 
   nsresult SetNonClientMargins(const LayoutDeviceIntMargin&) override;
   void SetDrawsInTitlebar(bool aState);
+  void SetTitlebarRect();
   mozilla::LayoutDeviceIntCoord GetTitlebarRadius();
   LayoutDeviceIntRect GetTitlebarRect();
   void UpdateWindowDraggingRegion(
@@ -622,14 +623,10 @@ class nsWindow final : public nsBaseWidget {
   static GdkCursor* gsGtkCursorCache[eCursorCount];
 
   // If true, draw our own window titlebar.
-  //
-  // Needs to be atomic because GetTitlebarRect() gets called from non-main
-  // threads.
-  //
-  // FIXME(emilio): GetTitlebarRect() reads other things that TSAN doesn't
-  // catch because mDrawInTitlebar is false on automation ~always. We should
-  // probably make GetTitlebarRect() simpler / properly thread-safe.
-  mozilla::Atomic<bool, mozilla::Relaxed> mDrawInTitlebar{false};
+  bool mDrawInTitlebar = false;
+
+  mozilla::Mutex mTitlebarRectMutex;
+  LayoutDeviceIntRect mTitlebarRect MOZ_GUARDED_BY(mTitlebarRectMutex);
 
   mozilla::Mutex mDestroyMutex;