diff --git a/effects/diminactive/diminactive.cpp b/effects/diminactive/diminactive.cpp
--- a/effects/diminactive/diminactive.cpp
+++ b/effects/diminactive/diminactive.cpp
@@ -46,8 +46,6 @@
 
 DimInactiveEffect::DimInactiveEffect()
 {
-    m_activeWindow = nullptr;
-
     initConfig<DimInactiveConfig>();
     reconfigure(ReconfigureAll);
 
@@ -78,6 +76,9 @@
     m_dimKeepAbove = DimInactiveConfig::dimKeepAbove();
     m_dimByGroup = DimInactiveConfig::dimByGroup();
 
+    // Need to reset m_activeWindow in order to correctly initialize it.
+    m_activeWindow = nullptr;
+
     EffectWindow *activeWindow = effects->activeWindow();
     m_activeWindow = (activeWindow && canDimWindow(activeWindow))
         ? activeWindow