diff --git a/c/externs.h b/c/externs.h
index 68f9579834..7955078f7a 100644
--- a/c/externs.h
+++ b/c/externs.h
@@ -331,13 +331,13 @@ extern void S_handle_overflood PROTO((void));
 extern void S_handle_apply_overflood PROTO((void));
 extern void S_overflow PROTO((ptr tc, iptr frame_request));
 extern void S_error_reset PROTO((const char *s));
-extern void S_error_abort PROTO((const char *s)) NORETURN;
-extern void S_abnormal_exit PROTO((void)) NORETURN;
+extern NORETURN void S_error_abort PROTO((const char *s));
+extern NORETURN void S_abnormal_exit PROTO((void));
 extern void S_error PROTO((const char *who, const char *s));
 extern void S_error1 PROTO((const char *who, const char *s, ptr x));
 extern void S_error2 PROTO((const char *who, const char *s, ptr x, ptr y));
 extern void S_error3 PROTO((const char *who, const char *s, ptr x, ptr y, ptr z));
-extern void S_boot_error PROTO((const ptr who, ptr s, ptr args)) NORETURN;
+extern NORETURN void S_boot_error PROTO((const ptr who, ptr s, ptr args));
 extern void S_handle_docall_error PROTO((void));
 extern void S_handle_arg_error PROTO((void));
 extern void S_handle_nonprocedure_symbol PROTO((void));