diff --git a/modules/mol/alg/pymod/structure_analysis.py b/modules/mol/alg/pymod/structure_analysis.py
index 3e013e4791a975f7bbb38f7f15021da9992292ac..7cb7644d497af8a3210e2c62daa00bbed64328af 100644
--- a/modules/mol/alg/pymod/structure_analysis.py
+++ b/modules/mol/alg/pymod/structure_analysis.py
@@ -152,8 +152,8 @@ def CalculateDistanceDifferenceMatrix(sele1,sele2):
   for i,a1 in enumerate(sele1.atoms):
     for j,a2 in enumerate(sele2.atoms):
       if i>=j:continue
-      d1=geom.Distance(a1.pos,a2.pos)
-      d2=geom.Distance(sele2.atoms[i].pos,sele2.atoms[j].pos)
+      d1=ost.geom.Distance(a1.pos,a2.pos)
+      d2=ost.geom.Distance(sele2.atoms[i].pos,sele2.atoms[j].pos)
       M[i,j]=d2-d1
       M[j,i]=d2-d1
   return M