diff --git a/repertory/librepertory/src/providers/sia/sia_provider.cpp b/repertory/librepertory/src/providers/sia/sia_provider.cpp
index 751d2923..ef99cceb 100644
--- a/repertory/librepertory/src/providers/sia/sia_provider.cpp
+++ b/repertory/librepertory/src/providers/sia/sia_provider.cpp
@@ -210,7 +210,7 @@ auto sia_provider::get_file(const std::string &api_path, api_file &file) const
     auto size{
         std::accumulate(
             slabs.begin(), slabs.end(), std::uint64_t(0U),
-            [](std::uint64_t total_size, auto &&slab) -> std::uint64_t {
+            [](std::uint64_t total_size, const json &slab) -> std::uint64_t {
               return total_size + slab["Length"].get<std::uint64_t>();
             }),
     };