diff --git a/include/osr/ways.h b/include/osr/ways.h
index 163403c..b3ca11a 100644
--- a/include/osr/ways.h
+++ b/include/osr/ways.h
@@ -183,6 +183,8 @@ struct ways {
     return cista::mmap{(p_ / file).generic_string().c_str(), mode_};
   }
 
+  void sync();
+
   way_idx_t::value_t n_ways() const { return way_osm_idx_.size(); }
   node_idx_t::value_t n_nodes() const { return node_to_osm_.size(); }
 
diff --git a/src/extract.cc b/src/extract.cc
index b55708c..cd206fa 100644
--- a/src/extract.cc
+++ b/src/extract.cc
@@ -558,6 +558,9 @@ void extract(bool const with_platforms,
     reader.close();
   }
 
+  w.r_->write(out);
+  w.sync();
+
   w.connect_ways();
 
   auto r = std::vector<resolved_restriction>{};
diff --git a/src/ways.cc b/src/ways.cc
index 5782453..e183e27 100644
--- a/src/ways.cc
+++ b/src/ways.cc
@@ -141,6 +141,18 @@ void ways::connect_ways() {
   std::filesystem::remove(p_ / "tmp_node_in_way_idx_index.bin", e);
 }
 
+void ways::sync() {
+  node_to_osm_.mmap_.sync();
+  way_osm_idx_.mmap_.sync();
+  way_polylines_.data_.mmap_.sync();
+  way_polylines_.bucket_starts_.mmap_.sync();
+  way_osm_nodes_.data_.mmap_.sync();
+  way_osm_nodes_.bucket_starts_.mmap_.sync();
+  strings_.data_.mmap_.sync();
+  strings_.bucket_starts_.mmap_.sync();
+  way_names_.mmap_.sync();
+}
+
 cista::wrapped<ways::routing> ways::routing::read(
     std::filesystem::path const& p) {
   return cista::read<ways::routing>(p / "routing.bin");