Index: trunk/Mars/CMakeLists.txt
===================================================================
--- trunk/Mars/CMakeLists.txt	(revision 19833)
+++ trunk/Mars/CMakeLists.txt	(revision 19834)
@@ -184,6 +184,17 @@
 ENDIF()
 
+IF(ROOTSYS AND NOT ROOTSYS STREQUAL $ENV{ROOTSYS})
+   MESSAGE(WARNING
+      " \n"
+      " ROOT Version changed!\n"
+      " Present  ROOTSYS: $ENV{ROOTSYS}\n"
+      " Previous ROOTSYS: ${ROOTSYS}")
+   FILE(REMOVE thisroot.sh)
+ENDIF()
+
+SET(ROOTSYS $ENV{ROOTSYS} CACHE INTERNAL "Internal variable to check for consistency in ROOTSYS")
+
 # For convenience and easy tracking
-ADD_CUSTOM_COMMAND(OUTPUT thisroot.sh COMMAND ln -sf $ENV{ROOTSYS}/bin/thisroot.sh VERBATIM)
+ADD_CUSTOM_COMMAND(OUTPUT thisroot.sh COMMAND ln -sf ${ROOTSYS}/bin/thisroot.sh VERBATIM)
 ADD_CUSTOM_TARGET(thisroot ALL DEPENDS thisroot.sh)