diff --git a/dxflib_qcad/dl_dxf.cpp b/dxflib_qcad/dl_dxf.cpp
index a76cf1611f..28e2a96db2 100644
--- a/dxflib_qcad/dl_dxf.cpp
+++ b/dxflib_qcad/dl_dxf.cpp
@@ -1714,7 +1714,7 @@ bool DL_Dxf::handleLWPolylineData( DL_CreationInterface*    /*creationInterface*
                 vertices[4 * vertexIndex + (groupCode / 10 - 1)] = toReal( groupValue );
             }
         }
-        else if( groupCode==42 && vertexIndex<maxVertices )
+        else if( groupCode==42 && vertexIndex<maxVertices && vertexIndex >= 0 )
         {
             vertices[4 * vertexIndex + 3] = toReal( groupValue );
         }