diff --git a/libc/private/libc_logging.h b/libc/private/libc_logging.h
index 9fa5982..49a5a3c 100644
--- a/libc/private/libc_logging.h
+++ b/libc/private/libc_logging.h
@@ -79,6 +79,15 @@
 //
 
 int __libc_format_buffer(char* _Nonnull buf, size_t size, const char* _Nonnull fmt, ...) __printflike(3, 4);
+
+#if defined(__arm__) || defined(__aarch64__) || defined(__x86_64__)
+int __libc_format_buffer_va_list(char* _Nonnull buffer, size_t buffer_size,
+                                 const char* _Nonnull format, va_list args);
+#else // defined(__mips__) || defined(__i386__)
+int __libc_format_buffer_va_list(char* _Nonnull buffer, size_t buffer_size,
+                                 const char* _Nonnull format, va_list _Nonnull args);
+#endif
+
 int __libc_format_fd(int fd, const char* _Nonnull format , ...) __printflike(2, 3);
 int __libc_format_log(int pri, const char* _Nonnull tag, const char* _Nonnull fmt, ...) __printflike(3, 4);
 #if defined(__arm__) || defined(__aarch64__) || defined(__x86_64__)