diff -Naur ceph-13.2.5-orig/src/rgw/rgw_sync_log_trim.cc ceph-13.2.5/src/rgw/rgw_sync_log_trim.cc
--- ceph-13.2.5-orig/src/rgw/rgw_sync_log_trim.cc	2019-03-12 17:48:03.000000000 +0100
+++ ceph-13.2.5/src/rgw/rgw_sync_log_trim.cc	2019-04-19 11:30:48.000000000 +0200
@@ -351,7 +351,7 @@
   status->clear();
   // The initialisation below is required to silence a false positive
   // -Wmaybe-uninitialized warning
-  boost::optional<size_t> num_shards = boost::make_optional(false, 0UL);
+  boost::optional<size_t> num_shards = boost::make_optional(false, (size_t)0);
   for (auto peer = first; peer != last; ++peer) {
     const size_t peer_shards = peer->size();
     if (!num_shards) {