diff --git a/libc/async_safe/async_safe_log.cpp b/libc/async_safe/async_safe_log.cpp
index 5f22c74..207035a 100644
--- a/libc/async_safe/async_safe_log.cpp
+++ b/libc/async_safe/async_safe_log.cpp
@@ -424,13 +424,18 @@
   return buffer_len;
 }
 
-int async_safe_format_fd(int fd, const char* format, ...) {
+int async_safe_format_fd_va_list(int fd, const char* format, va_list args) {
   FdOutputStream os(fd);
+  out_vformat(os, format, args);
+  return os.total;
+}
+
+int async_safe_format_fd(int fd, const char* format, ...) {
   va_list args;
   va_start(args, format);
-  out_vformat(os, format, args);
+  int result = async_safe_format_fd_va_list(fd, format, args);
   va_end(args);
-  return os.total;
+  return result;
 }
 
 static int write_stderr(const char* tag, const char* msg) {
diff --git a/libc/async_safe/include/async_safe/log.h b/libc/async_safe/include/async_safe/log.h
index 415b48e..df68062 100644
--- a/libc/async_safe/include/async_safe/log.h
+++ b/libc/async_safe/include/async_safe/log.h
@@ -90,6 +90,7 @@
 int async_safe_format_buffer_va_list(char* buffer, size_t buffer_size, const char* format, va_list args);
 
 int async_safe_format_fd(int fd, const char* format , ...) __printflike(2, 3);
+int async_safe_format_fd_va_list(int fd, const char* format, va_list args);
 int async_safe_format_log(int pri, const char* tag, const char* fmt, ...) __printflike(3, 4);
 int async_safe_format_log_va_list(int pri, const char* tag, const char* fmt, va_list ap);
 int async_safe_write_log(int pri, const char* tag, const char* msg);