diff --git a/mercurial/cext/manifest.c b/mercurial/cext/manifest.c
--- a/mercurial/cext/manifest.c
+++ b/mercurial/cext/manifest.c
@@ -135,12 +135,22 @@ static int find_lines(lazymanifest *self
 	return 0;
 }
 
+static void lazymanifest_init_early(lazymanifest *self)
+{
+	self->pydata = NULL;
+	self->lines = NULL;
+	self->numlines = 0;
+	self->maxlines = 0;
+}
+
 static int lazymanifest_init(lazymanifest *self, PyObject *args)
 {
 	char *data;
 	Py_ssize_t len;
 	int err, ret;
 	PyObject *pydata;
+
+	lazymanifest_init_early(self);
 	if (!PyArg_ParseTuple(args, "S", &pydata)) {
 		return -1;
 	}
@@ -668,6 +678,7 @@ static lazymanifest *lazymanifest_copy(l
 	if (!copy) {
 		goto nomem;
 	}
+	lazymanifest_init_early(copy);
 	copy->numlines = self->numlines;
 	copy->livelines = self->livelines;
 	copy->dirty = false;
@@ -705,6 +716,7 @@ static lazymanifest *lazymanifest_filter
 	if (!copy) {
 		goto nomem;
 	}
+	lazymanifest_init_early(copy);
 	copy->dirty = true;
 	copy->lines = malloc(self->maxlines * sizeof(line));
 	if (!copy->lines) {