diff --git a/effects/diminactive/diminactive.cpp b/effects/diminactive/diminactive.cpp
--- a/effects/diminactive/diminactive.cpp
+++ b/effects/diminactive/diminactive.cpp
@@ -372,6 +372,12 @@
 void DimInactiveEffect::windowDeleted(EffectWindow *w)
 {
     m_forceDim.remove(w);
+
+    // FIXME: Sometimes we can miss the window close signal because KWin
+    // can activate a window that is not ready for painting and the window
+    // gets destroyed immediately. So, we have to remove active transitions
+    // for that window here, otherwise we'll crash in postPaintScreen.
+    m_transitions.remove(w);
 }
 
 void DimInactiveEffect::activeFullScreenEffectChanged()