diff --git a/libc/include/error.h b/libc/include/error.h
index 18ce379..05ce35d 100644
--- a/libc/include/error.h
+++ b/libc/include/error.h
@@ -33,14 +33,14 @@
 
 __BEGIN_DECLS
 
-void error(int, int, const char* _Nonnull, ...) __printflike(3, 4) __INTRODUCED_IN(23);
-void error_at_line(int, int, const char*, unsigned int, const char* _Nonnull, ...) __printflike(5, 6)
-  __INTRODUCED_IN(23);
-
-extern void (*error_print_progname)(void) __INTRODUCED_IN(23);
+extern void (* _Nullable 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);
 
+void error(int, int, const char* _Nonnull, ...) __printflike(3, 4) __INTRODUCED_IN(23);
+void error_at_line(int, int, const char* _Nullable, unsigned int, const char* _Nonnull, ...)
+    __printflike(5, 6) __INTRODUCED_IN(23);
+
 __END_DECLS
 
 #endif