diff --git a/source/blender/io/usd/intern/usd_reader_stage.cc b/source/blender/io/usd/intern/usd_reader_stage.cc
index 0c179ceae48..3ee5e666d38 100644
--- a/source/blender/io/usd/intern/usd_reader_stage.cc
+++ b/source/blender/io/usd/intern/usd_reader_stage.cc
@@ -355,7 +355,7 @@ void USDStageReader::fake_users_for_unused_materials()
 {
   /* Iterate over the imported materials and set a fake user for any unused
    * materials. */
-  for (const std::pair<std::string, std::string> &path_mat_pair : settings_.usd_path_to_mat_name) {
+  for (const std::pair<const std::string, std::string> &path_mat_pair : settings_.usd_path_to_mat_name) {
 
     std::map<std::string, Material *>::iterator mat_it = settings_.mat_name_to_mat.find(
         path_mat_pair.second);