diff --git a/conf/commonshrc b/conf/commonshrc
index 1eb0787..8ebc3c0 100644
--- a/conf/commonshrc
+++ b/conf/commonshrc
@@ -47,8 +47,9 @@ add_to PATH ~/.gem/ruby/1.8/bin
 add_to PATH ~/.gem/ruby/1.9.1/bin
 
 if [ -x /usr/bin/perl ]; then
-  add_myprefix_to PERL5LIB lib/perl/`perl -e 'printf"%vd\n",$^V'`
-  add_myprefix_to PERL5LIB share/perl/`perl -e 'printf"%vd\n",$^V'`
+  PERLVERSION="`perl -e 'printf"%vd\n",$^V'`"
+  add_myprefix_to PERL5LIB lib/perl/$PERLVERSION
+  add_myprefix_to PERL5LIB share/perl/$PERLVERSION
 fi
 
 add_myprefix_to R_LIBS lib/R:/usr/lib/R/site-library