diff --git a/src/pylorax/treebuilder.py b/src/pylorax/treebuilder.py
index dac64ee9..01ea2446 100644
--- a/src/pylorax/treebuilder.py
+++ b/src/pylorax/treebuilder.py
@@ -150,7 +150,7 @@ class TreeBuilder(BaseBuilder):
     def implantisomd5(self):
         for section, data in self.treeinfo_data.items():
             if 'boot.iso' in data:
-                iso = joinpaths(self.outputdir, data['boot.iso'])
+                iso = joinpaths(self.outroot, data['boot.iso'])
                 check_call(["implantisomd5", iso])