diff --git a/kcms/fonts/package/contents/ui/main.qml b/kcms/fonts/package/contents/ui/main.qml
--- a/kcms/fonts/package/contents/ui/main.qml
+++ b/kcms/fonts/package/contents/ui/main.qml
@@ -113,6 +113,7 @@
                 Layout.fillWidth: true
                 horizontalAlignment: Text.AlignHCenter
                 text: i18n("to")
+                enabled: excludeCheckBox.checked
             }
 
             QtControls.SpinBox {