diff --git a/libc/include/__llvm-libc-common.h b/libc/include/__llvm-libc-common.h
--- a/libc/include/__llvm-libc-common.h
+++ b/libc/include/__llvm-libc-common.h
@@ -17,6 +17,9 @@
 #undef __END_C_DECLS
 #define __END_C_DECLS }
 
+#undef _Noreturn
+#define _Noreturn [[noreturn]]
+
 #else // not __cplusplus
 
 #undef __BEGIN_C_DECLS
diff --git a/libc/spec/spec.td b/libc/spec/spec.td
--- a/libc/spec/spec.td
+++ b/libc/spec/spec.td
@@ -48,6 +48,9 @@
 def VoidPtr : PtrType<VoidType>;
 def SizeTType : NamedType<"size_t">;
 
+// _Noreturn is really not a type, but it is convenient to treat it as a type.
+def NoReturn : NamedType<"_Noreturn void">;
+
 class Macro<string name> {
   string Name = name;
 }