diff --git a/lib/TWiki/Plugins/DoxygenPlugin/build.pl b/lib/TWiki/Plugins/DoxygenPlugin/build.pl
index acc1ff3..180a4a8 100755
--- a/lib/TWiki/Plugins/DoxygenPlugin/build.pl
+++ b/lib/TWiki/Plugins/DoxygenPlugin/build.pl
@@ -3,7 +3,7 @@
 # Build for DoxygenPlugin
 #
 BEGIN {
-  foreach my $pc (split(/:/, $ENV{TWIKI_LIBS})) {
+  foreach my $pc (split(/:/, $ENV{FOSWIKI_LIBS})) {
     unshift @INC, $pc;
   }
 }