diff --git a/kcmkwin/kwinrules/ruleitem.h b/kcmkwin/kwinrules/ruleitem.h
--- a/kcmkwin/kwinrules/ruleitem.h
+++ b/kcmkwin/kwinrules/ruleitem.h
@@ -55,7 +55,8 @@
         StartEnabled       = 1u << 1,
         AffectsWarning     = 1u << 2,
         AffectsDescription = 1u << 3,
-        AllFlags           = 0b1111
+        SuggestionOnly     = 1u << 4,
+        AllFlags           = 0b11111
     };
 
 public:
diff --git a/kcmkwin/kwinrules/ruleitem.cpp b/kcmkwin/kwinrules/ruleitem.cpp
--- a/kcmkwin/kwinrules/ruleitem.cpp
+++ b/kcmkwin/kwinrules/ruleitem.cpp
@@ -99,7 +99,7 @@
 
 void RuleItem::setEnabled(bool enabled)
 {
-    m_enabled = enabled | hasFlag(AlwaysEnabled);
+    m_enabled = (enabled && !hasFlag(SuggestionOnly)) || hasFlag(AlwaysEnabled);
 }
 
 bool RuleItem::hasFlag(RuleItem::Flags flag) const
diff --git a/kcmkwin/kwinrules/rulesmodel.cpp b/kcmkwin/kwinrules/rulesmodel.cpp
--- a/kcmkwin/kwinrules/rulesmodel.cpp
+++ b/kcmkwin/kwinrules/rulesmodel.cpp
@@ -104,7 +104,7 @@
     case EnabledRole:
         return rule->isEnabled();
     case SelectableRole:
-        return !rule->hasFlag(RuleItem::AlwaysEnabled);
+        return !rule->hasFlag(RuleItem::AlwaysEnabled) && !rule->hasFlag(RuleItem::SuggestionOnly);
     case ValueRole:
         return rule->value();
     case TypeRole:
@@ -137,6 +137,11 @@
         rule->setEnabled(value.toBool());
         break;
     case ValueRole:
+        if (rule->key() == "wmclasshelper") {
+            setData(this->index(1), value, RulesModel::ValueRole);  // wmclass := value
+            setData(this->index(2), true, RulesModel::ValueRole);   // wmclasscomplete := true
+            break;
+        }
         if (value == rule->value()) {
             return true;
         }
@@ -200,7 +205,7 @@
 
 void RulesModel::setDescription(const QString &description)
 {
-    setData(index(0, 0), description, RulesModel::ValueRole);
+    setData(index(0), description, RulesModel::ValueRole);
 }
 
 QString RulesModel::defaultDescription() const
@@ -230,7 +235,6 @@
     return QString();
 }
 
-
 bool RulesModel::wmclassWarning() const
 {
     const bool no_wmclass = !m_rules["wmclass"]->isEnabled()
@@ -288,7 +292,9 @@
         KConfigSkeletonItem *configItem = settings->findItem(rule->key());
         KConfigSkeletonItem *configPolicyItem = settings->findItem(rule->policyKey());
 
-        Q_ASSERT (configItem);
+        if (!configItem) {
+            continue;
+        }
 
         if (rule->isEnabled()) {
             configItem->setProperty(rule->value());
@@ -370,6 +376,13 @@
                                                 QIcon::fromTheme("window")));
     wmclasscomplete->setFlag(RuleItem::AlwaysEnabled);
 
+    // Helper item to store the detected whole window class when detecting properties
+    auto wmclasshelper = addRule(new RuleItem(QLatin1String("wmclasshelper"),
+                                              RulePolicy::NoPolicy, RuleItem::String,
+                                              i18n("Window whole class"), i18n("Window matching"),
+                                              QIcon::fromTheme("window")));
+    wmclasshelper->setFlag(RuleItem::SuggestionOnly);
+
     auto types = addRule(new RuleItem(QLatin1String("types"),
                                       RulePolicy::NoPolicy, RuleItem::FlagsOption,
                                       i18n("Window types"), i18n("Window matching"),
@@ -618,10 +631,6 @@
 const QHash<QString, QString> RulesModel::x11PropertyHash()
 {
     static const auto propertyToRule = QHash<QString, QString> {
-        /* The original detection dialog allows to choose depending on "Match complete window class":
-         *     if Match Complete == false: wmclass = "resourceClass"
-         *     if Match Complete == true:  wmclass = "resourceName" + " " + "resourceClass"
-         */
         { "resourceName",       "wmclass"       },
         { "caption",            "title"         },
         { "role",               "windowrole"    },
@@ -661,6 +670,12 @@
     }
     m_rules["types"]->setSuggestedValue(1 << window_type, forceValue);
 
+    // Store "complete window class" as "resourceName" + " " + "resourceClass"
+    // Do not force the value, we want it only as a suggested value for the user to select
+    const QString wmcompleteclass = QStringLiteral("%1 %2").arg(info.value("resourceName").toString())
+                                                           .arg(info.value("resourceClass").toString());
+    m_rules["wmclasshelper"]->setSuggestedValue(wmcompleteclass);
+
     const auto ruleForProperty = x11PropertyHash();
     for (QString &property : info.keys()) {
         if (!ruleForProperty.contains(property)) {