diff --git a/vp9/encoder/vp9_write_bit_buffer.c b/vp9/encoder/vp9_write_bit_buffer.c
index 962d0ca..6d55e84 100644
--- a/vp9/encoder/vp9_write_bit_buffer.c
+++ b/vp9/encoder/vp9_write_bit_buffer.c
@@ -8,9 +8,10 @@
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
+#include <limits.h>
 #include "vp9/encoder/vp9_write_bit_buffer.h"
 
-size_t vp9_rb_bytes_written(struct vp9_write_bit_buffer *wb) {
+size_t vp9_wb_bytes_written(const struct vp9_write_bit_buffer *wb) {
   return wb->bit_offset / CHAR_BIT + (wb->bit_offset % CHAR_BIT > 0);
 }