diff --git a/src/octTree.cpp b/src/octTree.cpp
index 30e0175..91648cf 100644
--- a/src/octTree.cpp
+++ b/src/octTree.cpp
@@ -19,6 +19,19 @@ OctTree::OctTree(const FCoordinates *particles, octPtr numParticles,
   //#ifdef VERBOSE
   cerr << "Allocating " << numCells << " octtree cells" << endl;
   //#endif
+  
+  for (int j = 0; j < 3; j++)
+    xMin[j] = particles[0][j];
+
+  for (octPtr i = 1; i < numParticles; i++)
+    {
+      for (int j = 0; j < 3; j++)
+	{
+	  if (particles[i][j] < xMin[j])
+	    xMin[j] = particles[i][j];      
+	}
+    }
+  
 
   cells = new OctCell[numCells];
   Lbox = (float)(octCoordTypeNorm+1);
diff --git a/src/octTree.hpp b/src/octTree.hpp
index 3aee37c..2402a5e 100644
--- a/src/octTree.hpp
+++ b/src/octTree.hpp
@@ -62,6 +62,8 @@ namespace CosmoTool
     float Lbox;
     octPtr lastNode;
     octPtr numCells;  
+    float lenNorm;
+    float xMin[3];
 
 
     template<typename FunT>
@@ -70,10 +72,13 @@ namespace CosmoTool
 			  octCoordType halfNodeLength)
     {
       OctCoords newCoord;
-      FCoordinates realCenter;
+      FCoordinates center, realCenter;
 
       for (int j = 0; j < 3; j++)
-	realCenter[j] = icoord[j]/(2.*octCoordCenter);
+	{
+	  center[j] = icoord[j]/(2.*octCoordCenter);
+	  realCenter[j] = center[j]*lenNorm+xMin[j];
+	}
       
       f(realCenter, cells[node].numberLeaves, halfNodeLength/(float)octCoordCenter,
 	cells[node].children[0] == invalidOctCell, // True if this is a meta-node
@@ -93,7 +98,10 @@ namespace CosmoTool
 	  if (newNode & octParticleMarker)
 	    {
 	      for (int j = 0; j < 3; j++)
-		realCenter[j] = newCoord[j]/(2.*octCoordCenter);
+		{
+		  center[j] = newCoord[j]/(2.*octCoordCenter);
+		  realCenter[j] = xMin[j] + lenNorm*center[j];
+		}
 
 	      f(realCenter, 
 		1, halfNodeLength/(2.*octCoordCenter),