diff --git a/src/server/internalServer.cpp b/src/server/internalServer.cpp
index 812b2bde9..d6e6a91a4 100644
--- a/src/server/internalServer.cpp
+++ b/src/server/internalServer.cpp
@@ -633,6 +633,21 @@ std::unique_ptr<Response> InternalServer::build_homepage(const RequestContext& r
  * Archive and Zim handlers begin
  **/
 
+class InternalServer::LockableSuggestionSearcher : public zim::SuggestionSearcher
+{
+  public:
+    explicit LockableSuggestionSearcher(const zim::Archive& archive)
+      : zim::SuggestionSearcher(archive)
+    {}
+
+    std::unique_lock<std::mutex> getLock() {
+      return std::unique_lock<std::mutex>(m_mutex);
+    }
+    virtual ~LockableSuggestionSearcher() = default;
+  private:
+    std::mutex m_mutex;
+};
+
 std::unique_ptr<Response> InternalServer::handle_suggest(const RequestContext& request)
 {
   if (m_verbose.load()) {
@@ -676,8 +691,9 @@ std::unique_ptr<Response> InternalServer::handle_suggest(const RequestContext& r
 
   /* Get the suggestions */
   auto searcher = suggestionSearcherCache.getOrPut(bookId,
-    [=](){ return make_shared<zim::SuggestionSearcher>(*archive); }
+    [=](){ return make_shared<LockableSuggestionSearcher>(*archive); }
   );
+  const auto lock(searcher->getLock());
   auto search = searcher->suggest(queryString);
   auto srs = search.getResults(start, count);
 
diff --git a/src/server/internalServer.h b/src/server/internalServer.h
index a73a7d424..6f523336e 100644
--- a/src/server/internalServer.h
+++ b/src/server/internalServer.h
@@ -88,9 +88,6 @@ class SearchInfo {
 
 
 typedef kainjow::mustache::data MustacheData;
-typedef ConcurrentCache<SearchInfo, std::shared_ptr<zim::Search>> SearchCache;
-typedef ConcurrentCache<std::string, std::shared_ptr<zim::SuggestionSearcher>> SuggestionSearcherCache;
-
 class OPDSDumper;
 
 class InternalServer {
@@ -157,6 +154,11 @@ class InternalServer {
 
     bool isLocallyCustomizedResource(const std::string& url) const;
 
+  private: // types
+    class LockableSuggestionSearcher;
+    typedef ConcurrentCache<SearchInfo, std::shared_ptr<zim::Search>> SearchCache;
+    typedef ConcurrentCache<std::string, std::shared_ptr<LockableSuggestionSearcher>> SuggestionSearcherCache;
+
   private: // data
     std::string m_addr;
     int m_port;