diff --git a/object_file.cc b/object_file.cc
index 64f8bdb1..9685dfe4 100644
--- a/object_file.cc
+++ b/object_file.cc
@@ -1176,7 +1176,8 @@ void ObjectFile<E>::write_symtab(Context<E> &ctx) {
 }
 
 bool is_c_identifier(std::string_view name) {
-  static std::regex re("[a-zA-Z_][a-zA-Z0-9_]*");
+  static std::regex re("[a-zA-Z_][a-zA-Z0-9_]*",
+                       std::regex_constants::optimize);
   return std::regex_match(name.begin(), name.end(), re);
 }
 
diff --git a/passes.cc b/passes.cc
index 4d98848d..fc3c7df1 100644
--- a/passes.cc
+++ b/passes.cc
@@ -311,7 +311,7 @@ void sort_init_fini(Context<E> &ctx) {
   Timer t(ctx, "sort_init_fini");
 
   auto get_priority = [](InputSection<E> *isec) {
-    static std::regex re(R"(_array\.(\d+)$)");
+    static std::regex re(R"(_array\.(\d+)$)", std::regex_constants::optimize);
     std::string name = isec->name().begin();
     std::smatch m;
     if (std::regex_search(name, m, re))