diff --git a/src/frontends/lean/parser.cpp b/src/frontends/lean/parser.cpp
index b33253662..10fcf2058 100644
--- a/src/frontends/lean/parser.cpp
+++ b/src/frontends/lean/parser.cpp
@@ -87,7 +87,7 @@ parser::parser(environment const & env, io_state const & ios,
     m_verbose(true), m_use_exceptions(use_exceptions),
     m_scanner(strm, strm_name, line), m_local_level_decls(lds), m_local_decls(eds),
     m_theorem_queue(*this, num_threads > 1 ? num_threads - 1 : 0),
-    m_snapshot_vector(sv), m_info_manager(im), m_cache(nullptr) {
+    m_snapshot_vector(sv), m_info_manager(im), m_cache(nullptr), m_index(nullptr) {
     m_num_threads = num_threads;
     m_no_undef_id_error    = false;
     m_found_errors = false;