diff --git a/src/pylorax/__init__.py b/src/pylorax/__init__.py
index 90224a4c..b3b06a33 100644
--- a/src/pylorax/__init__.py
+++ b/src/pylorax/__init__.py
@@ -188,13 +188,8 @@ class Lorax(BaseLoraxClass):
 
         buildstamp.write(joinpaths(self.inroot, ".buildstamp"))
 
-        dname = joinpaths(self.workdir, "pkglists")
-        if not os.path.isdir(dname):
-            os.makedirs(dname)
-        for pkgobj in ybo.doPackageLists(pkgnarrow='installed').installed:
-            with open(joinpaths(dname, pkgobj.name), "w") as fobj:
-                for fname in pkgobj.filelist + pkgobj.dirlist:
-                    fobj.write("{0}\n".format(fname))
+        if self.debug:
+            rb.writepkglists(joinpaths(self.workdir, "pkglists"))
 
         logger.info("doing post-install configuration")
         rb.postinstall()
diff --git a/src/pylorax/treebuilder.py b/src/pylorax/treebuilder.py
index 2aa70bfb..844d1de1 100644
--- a/src/pylorax/treebuilder.py
+++ b/src/pylorax/treebuilder.py
@@ -80,6 +80,15 @@ class RuntimeBuilder(object):
         '''Install packages and do initial setup with runtime-install.tmpl'''
         self._runner.run("runtime-install.tmpl")
 
+    def writepkglists(self, pkglistdir):
+        '''debugging data: write out lists of package contents'''
+        if not os.path.isdir(pkglistdir):
+            os.makedirs(pkglistdir)
+        for pkgobj in self.yum.doPackageLists(pkgnarrow='installed').installed:
+            with open(joinpaths(pkglistdir, pkgobj.name), "w") as fobj:
+                for fname in pkgobj.filelist + pkgobj.dirlist:
+                    fobj.write("{0}\n".format(fname))
+
     def postinstall(self):
         '''Do some post-install setup work with runtime-postinstall.tmpl'''
         # copy configdir into runtime root beforehand