--- a/widget/gtk/nsWindow.cpp
+++ b/widget/gtk/nsWindow.cpp
@@ -2396,17 +2396,19 @@ nsWindow::OnConfigureEvent(GtkWidget *aW
     //   the client window.
     //
     //   Override-redirect windows are children of the root window so parent
     //   coordinates are root coordinates.
 
     LOG(("configure event [%p] %d %d %d %d\n", (void *)this,
          aEvent->x, aEvent->y, aEvent->width, aEvent->height));
 
-    mPendingConfigures--;
+    if (mPendingConfigures > 0) {
+        mPendingConfigures--;
+    }
 
     LayoutDeviceIntRect screenBounds = GetScreenBounds();
 
     if (mWindowType == eWindowType_toplevel || mWindowType == eWindowType_dialog) {
         // This check avoids unwanted rollup on spurious configure events from
         // Cygwin/X (bug 672103).
         if (mBounds.x != screenBounds.x ||
             mBounds.y != screenBounds.y) {
@@ -4207,17 +4209,17 @@ nsWindow::NativeShow(bool aAction)
                 event.window = mGdkWindow;
                 event.send_event = TRUE;
                 event.x = allocation.x;
                 event.y = allocation.y;
                 event.width = allocation.width;
                 event.height = allocation.height;
 
                 auto shellClass = GTK_WIDGET_GET_CLASS(mShell);
-                for (int i = 0; i < mPendingConfigures; i++) {
+                for (unsigned int i = 0; i < mPendingConfigures; i++) {
                     Unused << shellClass->configure_event(mShell, &event);
                 }
                 mPendingConfigures = 0;
             }
 
             gtk_widget_hide(mShell);
 
             ClearTransparencyBitmap(); // Release some resources

--- a/widget/gtk/nsWindow.h
+++ b/widget/gtk/nsWindow.h
@@ -464,17 +464,17 @@ private:
     Window              mXWindow;
     Visual*             mXVisual;
     int                 mXDepth;
     mozilla::widget::WindowSurfaceProvider mSurfaceProvider;
 #endif
 
     // Upper bound on pending ConfigureNotify events to be dispatched to the
     // window. See bug 1225044.
-    int mPendingConfigures;
+    unsigned int mPendingConfigures;
 
 #ifdef ACCESSIBILITY
     RefPtr<mozilla::a11y::Accessible> mRootAccessible;
 
     /**
      * Request to create the accessible for this window if it is top level.
      */
     void                CreateRootAccessible();