diff --git a/libc/spec/spec.td b/libc/spec/spec.td
--- a/libc/spec/spec.td
+++ b/libc/spec/spec.td
@@ -39,6 +39,9 @@
 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;
 }