diff --git a/kcmkwin/kwindecoration/package/contents/ui/main.qml b/kcmkwin/kwindecoration/package/contents/ui/main.qml
--- a/kcmkwin/kwindecoration/package/contents/ui/main.qml
+++ b/kcmkwin/kwindecoration/package/contents/ui/main.qml
@@ -42,8 +42,16 @@
     implicitWidth: tabLayout.implicitWidth
     implicitHeight: tabLayout.implicitHeight
 
+    // TODO: replace this TabBar-plus-Frame-in-a-ColumnLayout with whatever shakes
+    // out of https://bugs.kde.org/show_bug.cgi?id=394296
     ColumnLayout {
         id: tabLayout
+
+        // Tab styles generally assume that they're touching the inner layout,
+        // not the frame, so we need to move the tab bar down a pixel and make
+        // sure it's drawn on top of the frame
+        Layout.bottomMargin: -1
+        z: 1
         anchors.fill: parent
         spacing: 0
         Controls.TabBar {