diff --git a/ecmascript/compiler/codegen/maple/maple_ir/include/parse_preg_no.h b/ecmascript/compiler/codegen/maple/maple_ir/include/parse_preg_no.h
new file mode 100644
index 0000000000..1a3a244f36
--- /dev/null
+++ b/ecmascript/compiler/codegen/maple/maple_ir/include/parse_preg_no.h
@@ -0,0 +1,40 @@
+/*
+ * Copyright (c) 2026 Huawei Device Co., Ltd.
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef PARSE_PREG_NO_H
+#define PARSE_PREG_NO_H
+
+#include <charconv>
+#include <cstdint>
+#include <string>
+#include <system_error>
+
+inline bool ParsePregNo(const std::string &s, uint32_t &out)
+{
+    if (s.empty()) {
+        return false;
+    }
+    uint32_t value = 0;
+    const char *first = s.data();
+    const char *last = first + s.size();
+    auto result = std::from_chars(first, last, value);
+    if (result.ec != std::errc() || result.ptr != last) {
+        return false;
+    }
+    out = value;
+    return true;
+}
+
+#endif
diff --git a/ecmascript/compiler/codegen/maple/maple_ir/src/mir_function.cpp b/ecmascript/compiler/codegen/maple/maple_ir/src/mir_function.cpp
index b826b54f25..2ddc668bba 100644
--- a/ecmascript/compiler/codegen/maple/maple_ir/src/mir_function.cpp
+++ b/ecmascript/compiler/codegen/maple/maple_ir/src/mir_function.cpp
@@ -14,7 +14,9 @@
  */
 
 #include "mir_function.h"
+#include "parse_preg_no.h"
 #include "printing.h"
+#include <cctype>
 
 namespace {
 using namespace maple;
@@ -440,12 +442,13 @@ void MIRFunction::EnterFormals()
         formalDef.formalSym->SetTyIdx(formalDef.formalTyIdx);
         formalDef.formalSym->SetAttrs(formalDef.formalAttrs);
         const std::string &formalName = GlobalTables::GetStrTable().GetStringFromStrIdx(formalDef.formalStrIdx);
-        if (!isdigit(formalName.front())) {
+        uint32 thepregno = 0;
+        if (formalName.empty() || !isdigit(static_cast<unsigned char>(formalName.front())) ||
+            !ParsePregNo(formalName, thepregno)) {
             formalDef.formalSym->SetSKind(kStVar);
             (void)symTab->AddToStringSymbolMap(*formalDef.formalSym);
         } else {
             formalDef.formalSym->SetSKind(kStPreg);
-            uint32 thepregno = static_cast<uint32>(std::stoi(formalName));
             MIRType *mirType = GlobalTables::GetTypeTable().GetTypeFromTyIdx(formalDef.formalTyIdx);
             PrimType pType = mirType->GetPrimType();
             // if mirType info is not needed, set mirType to nullptr