diff --git a/crypto/fift/utils.cpp b/crypto/fift/utils.cpp
index f37766a7..01cf0eb5 100644
--- a/crypto/fift/utils.cpp
+++ b/crypto/fift/utils.cpp
@@ -114,7 +114,7 @@ class MemoryFileLoader : public fift::FileLoader {
   std::map<std::string, std::string, std::less<>> files_;
 };
 
-td::Result<fift::SourceLookup> create_source_lookup(std::string main, bool need_preamble = true, bool need_asm = true,
+td::Result<fift::SourceLookup> create_source_lookup(std::string&& main, bool need_preamble = true, bool need_asm = true,
                                                     bool need_ton_util = true, bool need_lisp = true,
                                                     bool need_w3_code = true, bool need_fift_ext = true,
                                                     bool need_disasm = true, std::string dir = "") {
@@ -189,7 +189,7 @@ td::Result<fift::SourceLookup> run_fift(fift::SourceLookup source_lookup, std::o
 }  // namespace
 td::Result<FiftOutput> mem_run_fift(std::string source, std::vector<std::string> args, std::string fift_dir) {
   std::stringstream ss;
-  TRY_RESULT(source_lookup, create_source_lookup(source, true, true, true, true, true, true, true, fift_dir));
+  TRY_RESULT(source_lookup, create_source_lookup(std::move(source), true, true, true, true, true, true, true, fift_dir));
   TRY_RESULT_ASSIGN(source_lookup, run_fift(std::move(source_lookup), &ss, true, std::move(args)));
   FiftOutput res;
   res.source_lookup = std::move(source_lookup);
@@ -207,16 +207,21 @@ td::Result<FiftOutput> mem_run_fift(SourceLookup source_lookup, std::vector<std:
 td::Result<fift::SourceLookup> create_mem_source_lookup(std::string main, std::string fift_dir, bool need_preamble,
                                                         bool need_asm, bool need_ton_util, bool need_lisp,
                                                         bool need_w3_code) {
-  return create_source_lookup(main, need_preamble, need_asm, need_ton_util, need_lisp, need_w3_code, false, false,
+  return create_source_lookup(std::move(main), need_preamble, need_asm, need_ton_util, need_lisp, need_w3_code, false, false,
                               fift_dir);
 }
 
 td::Result<td::Ref<vm::Cell>> compile_asm(td::Slice asm_code, std::string fift_dir, bool is_raw) {
   std::stringstream ss;
-  TRY_RESULT(source_lookup,
-             create_source_lookup(PSTRING() << "\"Asm.fif\" include\n " << (is_raw ? "<{" : "") << asm_code << "\n"
-                                            << (is_raw ? "}>c" : "") << " boc>B \"res\" B>file",
-                                  true, true, true, false, false, false, false, fift_dir));
+  std::string sb;
+  sb.reserve(asm_code.size() + 100);
+  sb.append("\"Asm.fif\" include\n ");
+  sb.append(is_raw ? "<{" : "");
+  sb.append(asm_code.data(), asm_code.size());
+  sb.append(is_raw ? "}>c" : "");
+  sb.append(" boc>B \"res\" B>file");
+
+  TRY_RESULT(source_lookup, create_source_lookup(std::move(sb), true, true, true, false, false, false, false, fift_dir));
   TRY_RESULT(res, run_fift(std::move(source_lookup), &ss));
   TRY_RESULT(boc, res.read_file("res"));
   return vm::std_boc_deserialize(std::move(boc.data));