diff --git a/kded/daemon.cpp b/kded/daemon.cpp
--- a/kded/daemon.cpp
+++ b/kded/daemon.cpp
@@ -189,6 +189,15 @@
     }
     m_changeBlockTimer->invalidate();
     qCDebug(KSCREEN_KDED) << "Change detected";
+
+    // Modes may have changed, fix-up current mode id
+    Q_FOREACH(const KScreen::OutputPtr &output, m_monitoredConfig->outputs()) {
+        if (output->currentMode().isNull()) {
+            qCDebug(KSCREEN_KDED) << "Current mode invalid, fixing up mode id";
+            output->setCurrentModeId(output->preferredModeId());
+        }
+    }
+
     // Reset timer, delay the writeback
     m_saveTimer->start();
 }
@@ -199,6 +208,7 @@
 
     // We assume the config is valid, since it's what we got, but we are interested
     // in the "at least one enabled screen" check
+
     const bool valid = KScreen::Config::canBeApplied(m_monitoredConfig, KScreen::Config::ValidityFlag::RequireAtLeastOneEnabledScreen);
     if (valid) {
         Serializer::saveConfig(m_monitoredConfig, Serializer::configId(m_monitoredConfig));