diff --git a/scripts/package b/scripts/package
index 1fc9ec5a75..a5b3e915be 100755
--- a/scripts/package
+++ b/scripts/package
@@ -144,12 +144,13 @@ llvm() {
   __rvm_pushpop
 }
 
-if [[ ! -z "$library" ]] && is_a_function  ${library} ; then
-  ${library}
-else
-  if [[ ! -z "$library" ]] ; then
+if [[ ! -z "$library" ]] ; then
+  if [[ " readline iconv curl openssl zlib ncurses pkgconfig gettext glib mono llvm " =~ "$library" ]] ; then
+    ${library}
+  else
     $rvm_scripts_path/log "error" "Package '${library}' is unknown."
   fi
+else
   $rvm_scripts_path/log "info" "Usage: 'rvm package {install,uninstall} {openssl,zlib,readline,iconv,ncurses}'"
   exit 1
 fi