diff --git a/InnerDetector/InDetRecTools/SiSpacePointsSeedTool_xk/src/SiSpacePointsSeedMaker_ATLxk.cxx b/InnerDetector/InDetRecTools/SiSpacePointsSeedTool_xk/src/SiSpacePointsSeedMaker_ATLxk.cxx
index 058c193761e800e0e6a31f953beb324e1040c4bc..960487547cf719e0f862bb443ef01d8d2b3ca8a8 100644
--- a/InnerDetector/InDetRecTools/SiSpacePointsSeedTool_xk/src/SiSpacePointsSeedMaker_ATLxk.cxx
+++ b/InnerDetector/InDetRecTools/SiSpacePointsSeedTool_xk/src/SiSpacePointsSeedMaker_ATLxk.cxx
@@ -1850,7 +1850,13 @@ void InDet::SiSpacePointsSeedMaker_ATLxk::production3Sp
         * Note that below, the variable R is the radial coordinate fo the central SP, 
         * corresponding to r_central in the notation above. 
         **/
-        float d0  = std::abs((A-B*R)*R);
+	float d0 = 0;         
+	if(std::abs(B) < 1e-10) d0  = std::abs((A-B*R)*R);         
+	else{
+	  float x0 = -A/(2.*B);
+	  float rTrack = std::sqrt(onePlusAsquare/BSquare)*.5;
+	  d0 = std::abs(-rTrack + std::sqrt(rTrack*rTrack +2*x0*R +R*R));
+	}
 
         /// apply d0 cut to seed 
         if (d0 <= d0max) {
diff --git a/Tools/PROCTools/data/master_q431_AOD_digest.ref b/Tools/PROCTools/data/master_q431_AOD_digest.ref
index 6db7ca8af5ca03d22ee98135febdcdc6f46fa53f..534c155ff4c105636f11200debb4add11347d143 100644
--- a/Tools/PROCTools/data/master_q431_AOD_digest.ref
+++ b/Tools/PROCTools/data/master_q431_AOD_digest.ref
@@ -1,12 +1,12 @@
          run       event       nTopo   nIdTracks       nJets      nMuons
       330470  1183722158           1           0           0           0
-      330470  1183722342         394         414          18           0
+      330470  1183722342         394         414          20           0
       330470  1183727953         532         571          13           4
       330470  1183732647         467         452          13           1
       330470  1183733040         381         285           6           1
       330470  1183734651         361         363          14           3
-      330470  1183735332         406         370           9           1
-      330470  1183736475         741         650          17           2
+      330470  1183735332         406         371           9           1
+      330470  1183736475         741         651          17           2
       330470  1183738728           1           0           0           0
       330470  1183738949         368         418           9           1
       330470  1183742489         152         125           2           1
@@ -16,7 +16,7 @@
       330470  1183751782         239         235           5           0
       330470  1183752624         347         342           8           3
       330470  1183753006         357         377          11           3
-      330470  1183754806         470         405          14           0
+      330470  1183754806         470         406          14           0
       330470  1183769295         342         317           8           1
       330470  1183769939         348         341          11           3
       330470  1183773832         307         197           7           0