diff --git a/remotefilelog/debugcommands.py b/remotefilelog/debugcommands.py
--- a/remotefilelog/debugcommands.py
+++ b/remotefilelog/debugcommands.py
@@ -217,8 +217,10 @@
         hashlen = 14
 
     lastfilename = None
+    lastnode = None
     totaldeltasize = defaultdict(lambda: 0)
     totalblobsize = defaultdict(lambda: 0)
+    failures = 0
     def printtotals(filename):
         if not (filename in totaldeltasize or filename in totaldeltasize):
             return
@@ -256,9 +258,16 @@
             hashformatter(deltabase),
             str(deltalen).ljust(14),
             blobsize))
+        if not (deltabase == nullid or deltabase == lastnode):
+            ui.warn("^ BAD ENTRY\n")
+            failures += 1
+        lastnode = node
     if filename is not None:
         printtotals(filename)
 
+    if failures > 1:
+        ui.warn("\n%d invalid entries\n" % failures)
+        return 1
 
 def dumpdeltachain(ui, deltachain, **opts):
     hashformatter = hex
diff --git a/tests/test-treemanifest.t b/tests/test-treemanifest.t
--- a/tests/test-treemanifest.t
+++ b/tests/test-treemanifest.t
@@ -71,6 +71,7 @@
   (Root):
   Node          Delta Base    Delta Length  Blob Size
   70f2c6726cec  bc0c2c938b92  61            (missing)
+  ^ BAD ENTRY
 
 Test that commit creates local trees
   $ hg up -q tip