diff --git a/mercurial/revlog.py b/mercurial/revlog.py
--- a/mercurial/revlog.py
+++ b/mercurial/revlog.py
@@ -1432,9 +1432,9 @@ class revlog(object):
                 if self._isgooddelta(candidatedelta, textlen):
                     delta = candidatedelta
             if delta is None and self._generaldelta:
-                parents = [p1r, p2r]
                 # exclude already lazy tested base if any
-                parents = [p for p in parents if p not in tested]
+                parents = [p for p in (p1r, p2r)
+                           if p != nullrev and p not in tested]
                 if parents and not self._aggressivemergedeltas:
                     # Pick whichever parent is closer to us (to minimize the
                     # chance of having to build a fulltext).
diff --git a/tests/test-bundle.t b/tests/test-bundle.t
--- a/tests/test-bundle.t
+++ b/tests/test-bundle.t
@@ -266,13 +266,13 @@ Cannot produce streaming clone bundles w
 packed1 is produced properly
 
   $ hg -R test debugcreatestreamclonebundle packed.hg
-  writing 2667 bytes for 6 files
+  writing 2663 bytes for 6 files
   bundle requirements: generaldelta, revlogv1
 
   $ f -B 64 --size --sha1 --hexdump packed.hg
-  packed.hg: size=2830, sha1=c28255110a88ffa52ddc44985cad295b1ab349bc
+  packed.hg: size=2826, sha1=e139f97692a142b19cdcff64a69697d5307ce6d4
   0000: 48 47 53 31 55 4e 00 00 00 00 00 00 00 06 00 00 |HGS1UN..........|
-  0010: 00 00 00 00 0a 6b 00 16 67 65 6e 65 72 61 6c 64 |.....k..generald|
+  0010: 00 00 00 00 0a 67 00 16 67 65 6e 65 72 61 6c 64 |.....g..generald|
   0020: 65 6c 74 61 2c 72 65 76 6c 6f 67 76 31 00 64 61 |elta,revlogv1.da|
   0030: 74 61 2f 61 64 69 66 66 65 72 65 6e 74 66 69 6c |ta/adifferentfil|
 
diff --git a/tests/test-generaldelta.t b/tests/test-generaldelta.t
--- a/tests/test-generaldelta.t
+++ b/tests/test-generaldelta.t
@@ -133,8 +133,8 @@ Test format.aggressivemergedeltas
   $ hg debugindex -m
      rev    offset  length  delta linkrev nodeid       p1           p2
        0         0      59     -1       0 8dde941edb6e 000000000000 000000000000
-       1        59      59     -1       1 315c023f341d 000000000000 000000000000
-       2       118      65      1       2 2ab389a983eb 315c023f341d 8dde941edb6e
+       1        59      61      0       1 315c023f341d 000000000000 000000000000
+       2       120      65      1       2 2ab389a983eb 315c023f341d 8dde941edb6e
 
   $ hg strip -q -r . --config extensions.strip=
 
@@ -145,8 +145,8 @@ Test format.aggressivemergedeltas
   $ hg debugindex -m
      rev    offset  length  delta linkrev nodeid       p1           p2
        0         0      59     -1       0 8dde941edb6e 000000000000 000000000000
-       1        59      59     -1       1 315c023f341d 000000000000 000000000000
-       2       118      62      0       2 2ab389a983eb 315c023f341d 8dde941edb6e
+       1        59      61      0       1 315c023f341d 000000000000 000000000000
+       2       120      62      0       2 2ab389a983eb 315c023f341d 8dde941edb6e
 
 Test that strip bundle use bundle2
   $ hg --config extensions.strip= strip .
diff --git a/tests/test-treemanifest.t b/tests/test-treemanifest.t
--- a/tests/test-treemanifest.t
+++ b/tests/test-treemanifest.t
@@ -276,14 +276,14 @@ Turning off treemanifest config has no e
   $ hg debugindex .hg/store/meta/dir1/00manifest.i
      rev    offset  length  delta linkrev nodeid       p1           p2
        0         0     125     -1       4 63c9c0557d24 000000000000 000000000000
-       1       125     131     -1       5 23d12a1f6e0e 000000000000 000000000000
+       1       125     109      0       5 23d12a1f6e0e 000000000000 000000000000
   $ echo 2 > dir1/a
   $ hg --config experimental.treemanifest=False ci -qm 'modify dir1/a'
   $ hg debugindex .hg/store/meta/dir1/00manifest.i
      rev    offset  length  delta linkrev nodeid       p1           p2
        0         0     125     -1       4 63c9c0557d24 000000000000 000000000000
-       1       125     131     -1       5 23d12a1f6e0e 000000000000 000000000000
-       2       256      55      1       6 3cb2d87b4250 23d12a1f6e0e 000000000000
+       1       125     109      0       5 23d12a1f6e0e 000000000000 000000000000
+       2       234      55      1       6 3cb2d87b4250 23d12a1f6e0e 000000000000
 
 Create deeper repo with tree manifests.