diff --git a/mercurial/cext/revlog.c b/mercurial/cext/revlog.c
--- a/mercurial/cext/revlog.c
+++ b/mercurial/cext/revlog.c
@@ -1075,10 +1075,6 @@ static int nt_init(nodetree *self, index
 		return -1;
 	}
 	self->length = 1;
-	if (nt_insert(self, nullid, -1) == -1) {
-		free(self->nodes);
-		return -1;
-	}
 	return 0;
 }
 
@@ -1152,6 +1148,11 @@ static int index_init_nt(indexObject *se
 			self->nt = NULL;
 			return -1;
 		}
+		if (nt_insert(self->nt, nullid, -1) == -1) {
+			PyMem_Free(self->nt);
+			self->nt = NULL;
+			return -1;
+		}
 		self->ntrev = (int)index_length(self);
 		self->ntlookups = 1;
 		self->ntmisses = 0;
diff --git a/tests/test-revisions.t b/tests/test-revisions.t
--- a/tests/test-revisions.t
+++ b/tests/test-revisions.t
@@ -3,7 +3,7 @@
 
   $ echo 0 > a
   $ hg ci -qAm 0
-  $ for i in 5 8 14 43; do
+  $ for i in 5 8 14 43 167; do
   >   hg up -q 0
   >   echo $i > a
   >   hg ci -qm $i
@@ -14,6 +14,7 @@
   > EOF
 
   $ hg l
+  5:00f
   4:7ba5d
   3:7ba57
   2:72
@@ -21,9 +22,10 @@
   0:b
   $ cat <<EOF >> .hg/hgrc
   > [experimental]
-  > revisions.disambiguatewithin=:3
+  > revisions.disambiguatewithin=not 4
   > EOF
   $ hg l
+  5:0
   4:7ba5d
   3:7b
   2:72