diff --git a/redo-ifchange.py b/redo-ifchange.py
index be8aa7f..a3cc7a7 100755
--- a/redo-ifchange.py
+++ b/redo-ifchange.py
@@ -10,14 +10,11 @@ import vars, state, builder, jwack
 from helpers import unlink
 from log import debug, debug2, err
 
-def _nice(t):
-    return state.relpath(os.path.join(vars.BASE, t), vars.STARTDIR)
-
 CLEAN = 0
 DIRTY = 1
 def dirty_deps(f, depth, max_changed):
     if vars.DEBUG >= 1:
-        debug('%s?%s\n' % (depth, _nice(f.name)))
+        debug('%s?%s\n' % (depth, f.nicename()))
 
     if f.failed_runid:
         debug('%s-- DIRTY (failed last time)\n' % depth)
diff --git a/redo.py b/redo.py
index db4ba7b..ce9e3bc 100755
--- a/redo.py
+++ b/redo.py
@@ -39,9 +39,16 @@ import vars_init
 vars_init.init(targets)
 
 import vars, state, builder, jwack
-from log import err
+from log import warn, err
 
 try:
+    for t in targets:
+        if os.path.exists(t):
+            f = state.File(name=t)
+            if not f.is_generated:
+                warn('%s: exists and not marked as generated; not redoing.\n'
+                     % f.nicename())
+    
     j = atoi(opt.jobs or 1)
     if j < 1 or j > 1000:
         err('invalid --jobs value: %r\n' % opt.jobs)
diff --git a/state.py b/state.py
index ce43ad1..5eaf1ce 100644
--- a/state.py
+++ b/state.py
@@ -276,6 +276,10 @@ class File(object):
             # a "unique identifier" stamp for a regular file
             return str((st.st_ctime, st.st_mtime, st.st_size, st.st_ino))
 
+    def nicename(self):
+        return relpath(os.path.join(vars.BASE, self.name), vars.STARTDIR)
+
+
 
 # FIXME: I really want to use fcntl F_SETLK, F_SETLKW, etc here.  But python
 # doesn't do the lockdata structure in a portable way, so we have to use