diff --git a/lib/core/Handles/HandlesMatch.py b/lib/core/Handles/HandlesMatch.py
index 21ba577..ecca046 100644
--- a/lib/core/Handles/HandlesMatch.py
+++ b/lib/core/Handles/HandlesMatch.py
@@ -36,6 +36,27 @@ class MatchHandle(BaseHandle):
 
     def _HandleMatchLlvm(self, Node: ast.Match) -> None:
         Gen: "Translator.LlvmGen" = self.Trans.LlvmGen
+        # 重名 case 检测（fail-fast）：C 的 switch 不允许重复 case 标签——重复标签会让
+        # 某个臂永远不可达，且通常意味着漏改的分支；`case _`（default）同样只允许一个。
+        # 在产出任何 IR 之前检查，保证报错即终止。
+        SeenLabels: dict[str, int] = {}
+        DefaultCount: int = 0
+        for ci, case in enumerate(Node.cases):
+            Key: str | None = MatchHandle._CaseLabelKey(case.pattern)
+            if Key is None:
+                if isinstance(case.pattern, ast.MatchAs) and case.pattern.pattern is None:
+                    DefaultCount += 1
+                continue
+            if Key in SeenLabels:
+                from lib.core.LLVMCG.FuncGen import FailFastError
+                raise FailFastError(
+                    f"match 出现重名 case：标签 '{Key}' 已在第 {SeenLabels[Key]} 个 case 使用，"
+                    f"第 {ci} 个 case 重复（C switch 不允许重复 case 标签）")
+            SeenLabels[Key] = ci
+        if DefaultCount > 1:
+            from lib.core.LLVMCG.FuncGen import FailFastError
+            raise FailFastError(
+                f"match 出现 {DefaultCount} 个 `case _`（default 只允许一个）")
         SubjectVal: ir.Value | None = self.HandleExprLlvm(Node.subject)
         if not SubjectVal:
             return