diff --git a/libavutil/random_seed.h b/libavutil/random_seed.h
index e67e6e38c4..8a47be9679 100644
--- a/libavutil/random_seed.h
+++ b/libavutil/random_seed.h
@@ -21,6 +21,7 @@
 #ifndef AVUTIL_RANDOM_SEED_H
 #define AVUTIL_RANDOM_SEED_H
 
+#include <stddef.h>
 #include <stdint.h>
 /**
  * @addtogroup lavu_crypto