diff --git a/src/ifcparse/file.cpp b/src/ifcparse/file.cpp
index b4a277d04a..c5a4012bda 100644
--- a/src/ifcparse/file.cpp
+++ b/src/ifcparse/file.cpp
@@ -361,6 +361,8 @@ ifcopenshell::impl::rocks_db_file_storage::rocksdb_types_iterator::value_type co
 
 express::Base ifcopenshell::impl::rocks_db_file_storage::assert_existance(size_t number, instance_ref r) {
 #ifdef IFOPSH_WITH_ROCKSDB
+    std::lock_guard<std::mutex> lock(instance_cache_mutex_);
+
     if (r == ifcopenshell::impl::rocks_db_file_storage::entityinstance_ref) {
         auto it = instance_cache_.find(number);
         if (it != instance_cache_.end()) {
diff --git a/src/ifcparse/parse.cpp b/src/ifcparse/parse.cpp
index a49932d8f5..a60adb883f 100644
--- a/src/ifcparse/parse.cpp
+++ b/src/ifcparse/parse.cpp
@@ -2872,6 +2872,7 @@ void ifcopenshell::file::unbatch() {
 void ifcopenshell::file::reset_identity_cache() {
     std::visit([](auto& x) {
         if constexpr (std::is_same_v<std::decay_t<decltype(x)>, impl::rocks_db_file_storage>) {
+            std::lock_guard<std::mutex> lock(x.instance_cache_mutex_);
             x.instance_cache_.clear();
             x.type_instance_cache_.clear();
         }
diff --git a/src/ifcparse/storage.h b/src/ifcparse/storage.h
index c9f09638b4..50cf35a890 100644
--- a/src/ifcparse/storage.h
+++ b/src/ifcparse/storage.h
@@ -35,6 +35,7 @@ namespace rocksdb {
 #include <vector>
 #include <deque>
 #include <list>
+#include <mutex>
 #include <set>
 
 #ifndef SWIG
@@ -354,6 +355,7 @@ namespace ifcopenshell {
             // @todo this is silly, but we cannot have the same type, this should be just a pointer then on the file side?
             typedef std::map<uint32_t, std::shared_ptr<instance_data>> entity_by_iden_cache_t;
             entity_by_iden_cache_t instance_cache_, type_instance_cache_;
+            std::mutex instance_cache_mutex_;
 
             // @todo all these size_ts should probably be uint32_t for consistency with in-mem storage