diff --git a/inputcontext/QskHunspellTextPredictor.h b/inputcontext/QskHunspellTextPredictor.h
index 01e5832d..9631631c 100644
--- a/inputcontext/QskHunspellTextPredictor.h
+++ b/inputcontext/QskHunspellTextPredictor.h
@@ -14,7 +14,7 @@ class QSK_EXPORT QskHunspellTextPredictor : public QskTextPredictor
     using Inherited = QskTextPredictor;
 
 public:
-    QskHunspellTextPredictor( QObject* );
+    QskHunspellTextPredictor( QObject* = nullptr );
     virtual ~QskHunspellTextPredictor() override;
 
     virtual int candidateCount() const override;
diff --git a/inputcontext/QskPinyinTextPredictor.h b/inputcontext/QskPinyinTextPredictor.h
index 586505db..9199af71 100644
--- a/inputcontext/QskPinyinTextPredictor.h
+++ b/inputcontext/QskPinyinTextPredictor.h
@@ -14,7 +14,7 @@ class QSK_EXPORT QskPinyinTextPredictor : public QskTextPredictor
     using Inherited = QskTextPredictor;
 
 public:
-    QskPinyinTextPredictor( QObject* );
+    QskPinyinTextPredictor( QObject* = nullptr );
     virtual ~QskPinyinTextPredictor() override;
 
     virtual int candidateCount() const override;