diff --git a/src/scaffoldmaker/meshtypes/meshtype_3d_colon1.py b/src/scaffoldmaker/meshtypes/meshtype_3d_colon1.py
index 3d714fa7..e3f5299a 100644
--- a/src/scaffoldmaker/meshtypes/meshtype_3d_colon1.py
+++ b/src/scaffoldmaker/meshtypes/meshtype_3d_colon1.py
@@ -6,6 +6,7 @@
 
 import copy
 
+from cmlibs.maths.vectorops import magnitude
 from cmlibs.zinc.element import Element
 from cmlibs.zinc.field import Field
 from cmlibs.zinc.node import Node