Index: /trunk/Mars/CMakeLists.txt
===================================================================
--- /trunk/Mars/CMakeLists.txt	(revision 19853)
+++ /trunk/Mars/CMakeLists.txt	(revision 19854)
@@ -186,5 +186,5 @@
 
 # Is this is a local or a global installation?
-IF(ENV{ROOTSYS})
+IF(DEFINED ENV{ROOTSYS})
    IF(ROOTSYS AND NOT ROOTSYS STREQUAL "$ENV{ROOTSYS}")
       MESSAGE(WARNING