diff --git a/subcmds/diff.py b/subcmds/diff.py
index 1f3abd8..fa41e70 100644
--- a/subcmds/diff.py
+++ b/subcmds/diff.py
@@ -37,5 +37,8 @@
                  help='Paths are relative to the repository root')
 
   def Execute(self, opt, args):
+    ret = 0
     for project in self.GetProjects(args):
-      project.PrintWorkTreeDiff(opt.absolute)
+      if not project.PrintWorkTreeDiff(opt.absolute):
+        ret = 1
+    return ret