diff --git a/libavformat/aviobuf.c b/libavformat/aviobuf.c
index ac7bb8f7fd..46458db20f 100644
--- a/libavformat/aviobuf.c
+++ b/libavformat/aviobuf.c
@@ -711,7 +711,7 @@ typedef struct DynBuffer {
 static int dyn_buf_write(void *opaque, uint8_t *buf, int buf_size)
 {
     DynBuffer *d = opaque;
-    int new_size, new_allocated_size;
+    unsigned new_size, new_allocated_size;
 
     /* reallocate buffer if needed */
     new_size = d->pos + buf_size;