Index: library/lib/mkIndex.tcl
===================================================================
diff -u -rb34996b24ea334963e83aadda66384680a6f8ce5 -rb1379117656a8f4a9eb8aac043370fe8a299837e
--- library/lib/mkIndex.tcl	(.../mkIndex.tcl)	(revision b34996b24ea334963e83aadda66384680a6f8ce5)
+++ library/lib/mkIndex.tcl	(.../mkIndex.tcl)	(revision b1379117656a8f4a9eb8aac043370fe8a299837e)
@@ -8,8 +8,12 @@
 # - auto_path is needed, when nx is loaded via good old pkgIndex.tcl
 # - tcl::tm::roots is needed when nx is provided as a tcl module (.tm)
 lappend auto_path ..
-::tcl::tm::roots [pwd]
 
+# Is support for Tcl modules available (>= Tcl 8.5)?
+if {[info commands ::tcl::tm::roots] ne ""} {
+    ::tcl::tm::roots [pwd]
+}
+
 set verbose 0
 
 proc mkIndex {} {