diff -r 633408a0f2e2 -r 7eea2e4109ae mercurial/cext/revlog.c
--- a/mercurial/cext/revlog.c	Fri Oct 27 23:29:29 2023 +0200
+++ b/mercurial/cext/revlog.c	Fri Oct 27 22:11:05 2023 +0200
@@ -3037,7 +3037,7 @@
 	self->offsets = NULL;
 	self->nodelen = 20;
 	self->nullentry = NULL;
-	self->rust_ext_compat = 1;
+	self->rust_ext_compat = 0;
 	self->format_version = format_v1;
 
 	if (!PyArg_ParseTupleAndKeywords(args, kwargs, "OO|l", kwlist,
@@ -3055,6 +3055,7 @@
 	}
 
 	if (self->format_version == format_v1) {
+		self->rust_ext_compat = 1;
 		self->entry_size = v1_entry_size;
 	} else if (self->format_version == format_v2) {
 		self->entry_size = v2_entry_size;