diff --git a/src/commands/CmdUndo.cpp b/src/commands/CmdUndo.cpp
index 0097dda74..6dc451dce 100644
--- a/src/commands/CmdUndo.cpp
+++ b/src/commands/CmdUndo.cpp
@@ -45,9 +45,9 @@ CmdUndo::CmdUndo ()
 int CmdUndo::execute (std::string& output)
 {
   // Detect attempts to modify the task.
-  std::vector <Tree*>::iterator i;
-  for (i = context.parser.tree ()->_branches.begin (); i != context.parser.tree ()->_branches.end (); ++i)
-    if ((*i)->hasTag ("MODIFICATION"))
+  std::vector <A>::iterator a;
+  for (a = context.cli._args.begin (); a != context.cli._args.end (); ++a)
+    if (a->hasTag ("MODIFICATION"))
       throw std::string (STRING_CMD_UNDO_MODS);
 
   context.tdb2.revert ();