diff --git a/libavcodec/aarch64/idct.h b/libavcodec/aarch64/idct.h
index 5c49046148..97ee0a64af 100644
--- a/libavcodec/aarch64/idct.h
+++ b/libavcodec/aarch64/idct.h
@@ -19,6 +19,7 @@
 #ifndef AVCODEC_AARCH64_IDCT_H
 #define AVCODEC_AARCH64_IDCT_H
 
+#include <stddef.h>
 #include <stdint.h>
 
 void ff_simple_idct_neon(int16_t *data);