diff --git a/src/core/geometry/qgscompoundcurve.cpp b/src/core/geometry/qgscompoundcurve.cpp
index 0a70b12afb6..5bdd17190c1 100644
--- a/src/core/geometry/qgscompoundcurve.cpp
+++ b/src/core/geometry/qgscompoundcurve.cpp
@@ -436,7 +436,7 @@ void QgsCompoundCurve::removeCurve( int i )
 
 void QgsCompoundCurve::addVertex( const QgsPoint &pt )
 {
-  if ( mWkbType == QgsWkbTypes::Unknown )
+  if ( mCurves.isEmpty() || mWkbType == QgsWkbTypes::Unknown )
   {
     setZMTypeFromSubGeometry( &pt, QgsWkbTypes::CompoundCurve );
   }