diff --git a/qqmlsortfilterproxymodel.cpp b/qqmlsortfilterproxymodel.cpp
index 3ebca88..4e87ff1 100644
--- a/qqmlsortfilterproxymodel.cpp
+++ b/qqmlsortfilterproxymodel.cpp
@@ -350,10 +350,10 @@ bool QQmlSortFilterProxyModel::lessThan(const QModelIndex& source_left, const QM
 {
     if (m_completed) {
         if (!m_sortRoleName.isEmpty()) {
-            if (QSortFilterProxyModel::lessThan(source_left, source_right))
-                return m_ascendingSortOrder;
-            if (QSortFilterProxyModel::lessThan(source_right, source_left))
-                return !m_ascendingSortOrder;
+            if (m_ascendingSortOrder)
+                return QSortFilterProxyModel::lessThan(source_left, source_right);
+            else
+                return QSortFilterProxyModel::lessThan(source_right, source_left);
         }
         auto sortedSorters = m_sorters;
         std::stable_sort(sortedSorters.begin(),
@@ -364,8 +364,7 @@ bool QQmlSortFilterProxyModel::lessThan(const QModelIndex& source_left, const QM
         for(auto sorter : sortedSorters) {
             if (sorter->enabled()) {
                 int comparison = sorter->compareRows(source_left, source_right, *this);
-                if (comparison != 0)
-                    return comparison < 0;
+                return comparison == -1;
             }
         }
     }
diff --git a/sorters/expressionsorter.cpp b/sorters/expressionsorter.cpp
index 0d2904d..2e4c230 100644
--- a/sorters/expressionsorter.cpp
+++ b/sorters/expressionsorter.cpp
@@ -59,6 +59,7 @@ void ExpressionSorter::setExpression(const QQmlScriptString& scriptString)
 
 void ExpressionSorter::proxyModelCompleted(const QQmlSortFilterProxyModel& proxyModel)
 {
+    Sorter::proxyModelCompleted(proxyModel);
     updateContext(proxyModel);
 }
 
diff --git a/sorters/filtersorter.cpp b/sorters/filtersorter.cpp
index 29025f1..d902dd2 100644
--- a/sorters/filtersorter.cpp
+++ b/sorters/filtersorter.cpp
@@ -48,6 +48,8 @@ int FilterSorter::compare(const QModelIndex& sourceLeft, const QModelIndex& sour
 
 void FilterSorter::proxyModelCompleted(const QQmlSortFilterProxyModel& proxyModel)
 {
+    Sorter::proxyModelCompleted(proxyModel);
+
     for (Filter* filter : qAsConst(m_filters))
         filter->proxyModelCompleted(proxyModel);
 }
diff --git a/sorters/sorter.cpp b/sorters/sorter.cpp
index e9d0547..6e7e36e 100644
--- a/sorters/sorter.cpp
+++ b/sorters/sorter.cpp
@@ -107,21 +107,20 @@ void Sorter::setPriority(int priority)
 
 int Sorter::compareRows(const QModelIndex &source_left, const QModelIndex &source_right, const QQmlSortFilterProxyModel& proxyModel) const
 {
-    int comparison = compare(source_left, source_right, proxyModel);
-    return (m_sortOrder == Qt::AscendingOrder) ? comparison : -comparison;
+    if (m_sortOrder == Qt::AscendingOrder)
+        return compare(source_left, source_right, proxyModel);
+    else
+        return compare(source_right, source_left, proxyModel);
 }
 
 int Sorter::compare(const QModelIndex &sourceLeft, const QModelIndex &sourceRight, const QQmlSortFilterProxyModel& proxyModel) const
 {
-    if (lessThan(sourceLeft, sourceRight, proxyModel))
-        return -1;
-    if (lessThan(sourceRight, sourceLeft, proxyModel))
-        return 1;
-    return 0;
+    return lessThan(sourceLeft, sourceRight, proxyModel) ? -1 : 1;
 }
 
 void Sorter::proxyModelCompleted(const QQmlSortFilterProxyModel& proxyModel)
 {
+    m_proxyCompleted = true;
     Q_UNUSED(proxyModel)
 }
 
@@ -135,7 +134,7 @@ bool Sorter::lessThan(const QModelIndex &sourceLeft, const QModelIndex &sourceRi
 
 void Sorter::invalidate()
 {
-    if (m_enabled)
+    if (m_enabled && m_proxyCompleted)
         Q_EMIT invalidated();
 }
 
diff --git a/sorters/sorter.h b/sorters/sorter.h
index f7ecd88..db9ddac 100644
--- a/sorters/sorter.h
+++ b/sorters/sorter.h
@@ -45,12 +45,14 @@ Q_SIGNALS:
 protected:
     virtual int compare(const QModelIndex& sourceLeft, const QModelIndex& sourceRight, const QQmlSortFilterProxyModel& proxyModel) const;
     virtual bool lessThan(const QModelIndex& sourceLeft, const QModelIndex& sourceRight, const QQmlSortFilterProxyModel& proxyModel) const;
-    void invalidate();
+    virtual void invalidate();
 
 private:
     bool m_enabled = true;
     Qt::SortOrder m_sortOrder = Qt::AscendingOrder;
     int m_priority = 0;
+
+    bool m_proxyCompleted = false;
 };
 
 }