diff --git a/libavutil/fifo.c b/libavutil/fifo.c
index ca25bc5239..235b53ce40 100644
--- a/libavutil/fifo.c
+++ b/libavutil/fifo.c
@@ -51,12 +51,12 @@ void av_fifo_reset(AVFifoBuffer *f)
     f->wndx = f->rndx = 0;
 }
 
-int av_fifo_size(AVFifoBuffer *f)
+int av_fifo_size(const AVFifoBuffer *f)
 {
     return (uint32_t)(f->wndx - f->rndx);
 }
 
-int av_fifo_space(AVFifoBuffer *f)
+int av_fifo_space(const AVFifoBuffer *f)
 {
     return f->end - f->buffer - av_fifo_size(f);
 }
diff --git a/libavutil/fifo.h b/libavutil/fifo.h
index 849b9a6b81..fe7364f427 100644
--- a/libavutil/fifo.h
+++ b/libavutil/fifo.h
@@ -59,7 +59,7 @@ void av_fifo_reset(AVFifoBuffer *f);
  * @param f AVFifoBuffer to read from
  * @return size
  */
-int av_fifo_size(AVFifoBuffer *f);
+int av_fifo_size(const AVFifoBuffer *f);
 
 /**
  * Return the amount of space in bytes in the AVFifoBuffer, that is the
@@ -67,7 +67,7 @@ int av_fifo_size(AVFifoBuffer *f);
  * @param f AVFifoBuffer to write into
  * @return size
  */
-int av_fifo_space(AVFifoBuffer *f);
+int av_fifo_space(const AVFifoBuffer *f);
 
 /**
  * Feed data from an AVFifoBuffer to a user-supplied callback.