diff --git a/src/pylorax/instroot.py b/src/pylorax/instroot.py
index 0089367d..46aba9d8 100644
--- a/src/pylorax/instroot.py
+++ b/src/pylorax/instroot.py
@@ -96,7 +96,7 @@ def createInstRoot(yumconf=None, arch=None, treedir=None, updates=None):
     return True
 
 # Call yummain to install the list of packages to destdir
-def installPackages(yumconf=yumconf, destdir=destdir, packages=packages):
+def installPackages(yumconf=None, destdir=None, packages=None):
     """installPackages(yumconf=yumconf, destdir=destdir, packages=packages)
 
     Call yummain to install the list of packages.  All parameters are
@@ -111,6 +111,9 @@ def installPackages(yumconf=yumconf, destdir=destdir, packages=packages):
 
     """
 
+    if yumconf is None or destdir is None or packages is None or packages == []:
+        return False
+
     arglist = ['-c', yumconf, '-y']
     arglist.append("--installroot=%s" % (destdir,))
     arglist.append('install')