diff --git a/remotefilelog/debugcommands.py b/remotefilelog/debugcommands.py
--- a/remotefilelog/debugcommands.py
+++ b/remotefilelog/debugcommands.py
@@ -215,7 +215,6 @@
         hashformatter = short
         hashlen = 14
 
-    lastfilename = None
     totaldeltasize = 0
     totalblobsize = 0
     def printtotals():
@@ -233,6 +232,9 @@
             deltastr
         ))
 
+    lastfilename = None
+    seennodes = {nullid: True}
+    failures = 0
     for filename, node, deltabase, deltalen in dpack.iterentries():
         if filename != lastfilename:
             printtotals()
@@ -246,6 +248,7 @@
             lastfilename = filename
             totalblobsize = 0
             totaldeltasize = 0
+
         # Metadata could be missing, in which case it will be an empty dict.
         meta = dpack.getmeta(filename, node)
         if constants.METAKEYSIZE in meta:
@@ -259,8 +262,19 @@
             hashformatter(deltabase),
             str(deltalen).ljust(14),
             blobsize))
+
+        # The only integrity constraint is that all deltabases must exist
+        # earlier in the pack.
+        if not deltabase in seennodes:
+            ui.warn("^ BAD ENTRY - unknown delta base of %s\n" %
+                    short(deltabase))
+            failures += 1
+        seennodes[node] = True
     if filename is not None:
         printtotals()
+    if failures > 1:
+        ui.warn("\n%d invalid entries\n" % failures)
+        return 1
 
 def dumpdeltachain(ui, deltachain, **opts):
     hashformatter = hex