diff --git a/src/nodes/QskVertex.cpp b/src/nodes/QskVertex.cpp
index ff741668..7916b3e0 100644
--- a/src/nodes/QskVertex.cpp
+++ b/src/nodes/QskVertex.cpp
@@ -22,7 +22,7 @@ QDebug operator<<( QDebug debug, Color color )
     return debug;
 }
 
-QDebug operator<<( QDebug debug, ColoredLine line )
+QDebug operator<<( QDebug debug, const ColoredLine& line )
 {
     qDebug() << qRound( line.p1.x ) << qRound( line.p1.y )
         << "->" << qRound( line.p2.x ) << qRound( line.p2.y );
@@ -30,7 +30,7 @@ QDebug operator<<( QDebug debug, ColoredLine line )
     return debug;
 }
 
-QDebug operator<<( QDebug debug, Line line )
+QDebug operator<<( QDebug debug, const Line& line )
 {
     qDebug() << qRound( line.p1.x ) << qRound( line.p1.y )
         << "->" << qRound( line.p2.x ) << qRound( line.p2.y );
@@ -41,7 +41,7 @@ QDebug operator<<( QDebug debug, Line line )
 #endif
 
 template< class Line >
-static inline void qskDebugGeometry( Line* lines, int count )
+static inline void qskDebugGeometry( const Line* lines, int count )
 {
 #ifndef QT_NO_DEBUG_STREAM
     for ( int i = 0; i < count; i++ )
diff --git a/src/nodes/QskVertex.h b/src/nodes/QskVertex.h
index f1874bbd..0700d0ae 100644
--- a/src/nodes/QskVertex.h
+++ b/src/nodes/QskVertex.h
@@ -170,8 +170,8 @@ namespace QskVertex
 #ifndef QT_NO_DEBUG_STREAM
 class QDebug;
 QDebug operator<<( QDebug debug, QskVertex::Color );
-QDebug operator<<( QDebug debug, QskVertex::ColoredLine );
-QDebug operator<<( QDebug debug, QskVertex::Line );
+QDebug operator<<( QDebug debug, const QskVertex::ColoredLine& );
+QDebug operator<<( QDebug debug, const QskVertex::Line& );
 #endif
 
 #endif