diff --git a/Simulation/ISF/ISF_Core/ISF_Services/python/ISF_ServicesConfig.py b/Simulation/ISF/ISF_Core/ISF_Services/python/ISF_ServicesConfig.py
index f9219c91a877b541d810ac1d8d1bdb8e986ab924..049ea8cd4dc1cc0289f8b55ec9240b71377b2c4c 100644
--- a/Simulation/ISF/ISF_Core/ISF_Services/python/ISF_ServicesConfig.py
+++ b/Simulation/ISF/ISF_Core/ISF_Services/python/ISF_ServicesConfig.py
@@ -66,7 +66,7 @@ def getAFIIEnvelopeDefSvc(name="ISF_AFIIEnvelopeDefSvc", **kwargs):
     from AthenaCommon.SystemOfUnits import mm
     # ATLAS common envlope definitions
     kwargs.setdefault("ISFEnvelopeDefSvc"    , "ISF_ISFEnvelopeDefSvc"         )
-    kwargs.setdefault("InDetMaxExtentZ"      , 3550.*mm                        )
+    kwargs.setdefault("InDetMaxExtentZ"      , 3549.5*mm                       )
 
     from ISF_Services.ISF_ServicesConf import ISF__AFIIEnvelopeDefSvc
     return ISF__AFIIEnvelopeDefSvc(name, **kwargs)