diff --git a/EGkBBox3d.h b/EGkBBox3d.h
index ca8e799..f16ebea 100644
--- a/EGkBBox3d.h
+++ b/EGkBBox3d.h
@@ -35,11 +35,11 @@ class EGK_EXPORT BBox3d
       BBox3d( double dX, double dY, double dZ)
          : m_ptMin( dX, dY, dZ), m_ptMax( dX, dY, dZ) {}
       BBox3d( const Point3d& ptCen, double dDelta)
-         : m_ptMin( ptCen.x - dDelta, ptCen.y - dDelta, ptCen.z - dDelta),
-           m_ptMax( ptCen.x + dDelta, ptCen.y + dDelta, ptCen.z + dDelta)  {}
+         : m_ptMin( ptCen.x - abs( dDelta), ptCen.y - abs( dDelta), ptCen.z - abs( dDelta)),
+           m_ptMax( ptCen.x + abs( dDelta), ptCen.y + abs( dDelta), ptCen.z + abs( dDelta))  {}
       BBox3d( const Point3d& ptCen, double dDeltaX, double dDeltaY, double dDeltaZ)
-         : m_ptMin( ptCen.x - dDeltaX, ptCen.y - dDeltaY, ptCen.z - dDeltaZ),
-           m_ptMax( ptCen.x + dDeltaX, ptCen.y + dDeltaY, ptCen.z + dDeltaZ)  {}
+         : m_ptMin( ptCen.x - abs( dDeltaX), ptCen.y - abs( dDeltaY), ptCen.z - abs( dDeltaZ)),
+           m_ptMax( ptCen.x + abs( dDeltaX), ptCen.y + abs( dDeltaY), ptCen.z + abs( dDeltaZ))  {}
       BBox3d( const Point3d& ptP1, const Point3d& ptP2) ;
       BBox3d( double dX1, double dY1, double dZ1, double dX2, double dY2, double dZ2) ;
       void Reset( void)