diff --git a/effects/slidingpopups/slidingpopups.cpp b/effects/slidingpopups/slidingpopups.cpp
index 4f0a9ea11d..99c3bfe732 100644
--- a/effects/slidingpopups/slidingpopups.cpp
+++ b/effects/slidingpopups/slidingpopups.cpp
@@ -85,6 +85,11 @@ void SlidingPopupsEffect::prePaintWindow(EffectWindow* w, WindowPrePaintData& da
         } else {
             delete mAppearingWindows.take(w);
             w->setData(WindowForceBlurRole, false);
+            if (m_backgroundContrastForced.contains(w) && w->hasAlpha() &&
+                    w->data(WindowForceBackgroundContrastRole).toBool()) {
+                w->setData(WindowForceBackgroundContrastRole, QVariant());
+                m_backgroundContrastForced.removeAll(w);
+            }
         }
     } else if (mDisappearingWindows.contains(w)) {
 
@@ -255,6 +260,10 @@ void SlidingPopupsEffect::slotWindowAdded(EffectWindow *w)
 {
     slotPropertyNotify(w, mAtom);
     if (w->isOnCurrentDesktop() && mWindowsData.contains(w)) {
+        if (!w->data(WindowForceBackgroundContrastRole).isValid() && w->hasAlpha()) {
+            w->setData(WindowForceBackgroundContrastRole, QVariant(true));
+            m_backgroundContrastForced.append(w);
+        }
         mAppearingWindows.insert(w, new QTimeLine(mWindowsData[ w ].fadeInDuration, this));
         mAppearingWindows[ w ]->setCurveShape(QTimeLine::EaseInOutCurve);
 
@@ -278,9 +287,13 @@ void SlidingPopupsEffect::slotWindowClosed(EffectWindow* w)
         // Tell other windowClosed() effects to ignore this window
         w->setData(WindowClosedGrabRole, QVariant::fromValue(static_cast<void*>(this)));
         w->setData(WindowForceBlurRole, true);
+        if (!w->data(WindowForceBackgroundContrastRole).isValid() && w->hasAlpha()) {
+            w->setData(WindowForceBackgroundContrastRole, QVariant(true));
+        }
 
         w->addRepaintFull();
     }
+    m_backgroundContrastForced.removeAll(w);
 }
 
 void SlidingPopupsEffect::slotWindowDeleted(EffectWindow* w)
diff --git a/effects/slidingpopups/slidingpopups.h b/effects/slidingpopups/slidingpopups.h
index f66e42ec42..77f0103b49 100644
--- a/effects/slidingpopups/slidingpopups.h
+++ b/effects/slidingpopups/slidingpopups.h
@@ -74,6 +74,11 @@ private:
         int slideLength;
     };
     long mAtom;
+
+    // This list is only for appearing windows: we remember that we've enabled the
+    // WindowBackgroundContrastForcedRole flag, so we can remove it later.
+    // It doesn't matter for disappearing windows, they'll be deleted anyway.
+    QList< const EffectWindow* > m_backgroundContrastForced;
     QHash< const EffectWindow*, QTimeLine* > mAppearingWindows;
     QHash< const EffectWindow*, QTimeLine* > mDisappearingWindows;
     QHash< const EffectWindow*, Data > mWindowsData;