diff --git a/libc/include/error.h b/libc/include/error.h
index dd12884..205890f 100644
--- a/libc/include/error.h
+++ b/libc/include/error.h
@@ -33,12 +33,13 @@
 
 __BEGIN_DECLS
 
-void error(int, int, const char*, ...) __printflike(3, 4);
-void error_at_line(int, int, const char*, unsigned int, const char*, ...) __printflike(5, 6);
+void error(int, int, const char*, ...) __printflike(3, 4) __INTRODUCED_IN(23);
+void error_at_line(int, int, const char*, unsigned int, const char*, ...) __printflike(5, 6)
+  __INTRODUCED_IN(23);
 
-extern void (*error_print_progname)(void);
-extern unsigned int error_message_count;
-extern int error_one_per_line;
+extern void (*error_print_progname)(void) __INTRODUCED_IN(23);
+extern unsigned int error_message_count __INTRODUCED_IN(23);
+extern int error_one_per_line __INTRODUCED_IN(23);
 
 __END_DECLS