diff --git a/Modules/_json.c b/Modules/_json.c
index 4682cf8..8117d16 100644
--- a/Modules/_json.c
+++ b/Modules/_json.c
@@ -652,6 +652,7 @@
     Py_VISIT(self->parse_float);
     Py_VISIT(self->parse_int);
     Py_VISIT(self->parse_constant);
+    Py_VISIT(self->memo);
     return 0;
 }