diff --git a/lib/mu-server.cc b/lib/mu-server.cc
index f5f455fa..9aae7cfe 100644
--- a/lib/mu-server.cc
+++ b/lib/mu-server.cc
@@ -889,6 +889,7 @@ Server::Private::index_handler(const Command& cmd)
 		throw Error{Error::Code::Xapian, "indexer is already running"};
 
 	do_index(conf);
+	store().serialize();
 }
 
 void
diff --git a/lib/mu-store-labels.hh b/lib/mu-store-labels.hh
index b36c9bd1..df4dde02 100644
--- a/lib/mu-store-labels.hh
+++ b/lib/mu-store-labels.hh
@@ -17,7 +17,6 @@
 **
 */
 
-
 #ifndef MU_LABELS_CACHE_HH
 #define MU_LABELS_CACHE_HH
 
@@ -59,6 +58,7 @@ public:
 			label_map_.insert({label, 1});
 		else
 			++it->second;
+		dirty_ = true;
 	}
 	/**
 	 * Remove a label occurrence from the cache
@@ -73,6 +73,7 @@ public:
 				label_map_.erase(it);
 			else
 				--it->second;
+			dirty_ = true;
 		}
 	}
 
@@ -107,13 +108,15 @@ public:
 	/**
 	 * Serialize the cache into a string.
 	 *
+	 * Note: this also marks the cache a _non_ dirty;
+	 *
 	 * @return serialized cache
 	 */
-	std::string serialize() const {
+	[[nodiscard]] std::string serialize() const {
 		std::string s;
 		for (const auto&[label, n]: label_map_)
 			s += mu_format("{}{}{}\n", label, SepaChar2, n);
-
+		dirty_ = false;
 		return s;
 	}
 
@@ -140,8 +143,20 @@ public:
 		return map;
 	}
 
+	/**
+	 * Is the cache "dirty"?
+	 *
+	 * I.e. have there been changes since "serialize()" was called?
+	 *
+	 * @return true or false
+	 */
+	bool dirty() const {
+		return dirty_;
+	}
+
 private:
 	Map label_map_;
+	mutable bool dirty_{};
 };
 
 class Store;
diff --git a/lib/mu-store.cc b/lib/mu-store.cc
index 8d0f1219..0d4dba64 100644
--- a/lib/mu-store.cc
+++ b/lib/mu-store.cc
@@ -85,11 +85,11 @@ struct Store::Private {
 	}
 
 	~Private() try {
-		mu_debug("closing store @ {}", xapian_db_.path());
 		if (!xapian_db_.read_only()) {
-			contacts_cache_.serialize();
-			config_.set<Config::Id::Labels>(labels_cache_.serialize());
+			if (const auto res = serialize(); !res)
+				mu_critical("failed to serialize: {}", res.error().what());
 		}
+		mu_debug("closing store @ {}", xapian_db_.path());
 	} catch (...) {
 		mu_critical("caught exception in store dtor");
 	}
@@ -119,6 +119,8 @@ struct Store::Private {
 			return Message::Options::None;
 	}
 
+	Result<void> serialize();
+
 	Option<Message> find_message_unlocked(Store::Id docid) const;
 	Store::IdVec find_duplicates_unlocked(const Store& store,
 					      const std::string& message_id) const;
@@ -145,6 +147,23 @@ struct Store::Private {
 };
 
 
+Result<void>
+Store::Private::serialize()
+{
+	if (xapian_db_.read_only())
+		return Err(Error::Code::Store, "store must be writable");
+
+	mu_debug("serialize data into store @ {}", xapian_db_.path());
+
+	contacts_cache_.serialize(); // does the 'dirty' check internally.
+
+	if (labels_cache_.dirty())
+		config_.set<Config::Id::Labels>(labels_cache_.serialize());
+
+	return Ok();
+}
+
+
 Result<Store::Id>
 Store::Private::add_message_unlocked(Message& msg)
 {
@@ -335,6 +354,13 @@ Store::contacts_cache() const
 	return priv_->contacts_cache_;
 }
 
+Result<void>
+Store::serialize()
+{
+	std::lock_guard guard{priv_->lock_};
+	return priv_->serialize();
+}
+
 Indexer&
 Store::indexer()
 {
diff --git a/lib/mu-store.hh b/lib/mu-store.hh
index e23978be..555f2f03 100644
--- a/lib/mu-store.hh
+++ b/lib/mu-store.hh
@@ -140,6 +140,17 @@ public:
 	 */
 	const ContactsCache& contacts_cache() const;
 
+
+	/**
+	 * Serialize ephemeral information such as contacts, labels,
+	 * in the database.
+	 *
+	 * Only available when using a writable database.
+	 *
+	 * @return Ok() or some error.
+	 */
+	Result<void> serialize();
+
 	/**
 	 * Get the Indexer associated with this store. It is an error to call
 	 * this on a read-only store.