diff --git a/libavcodec/ac3dsp.h b/libavcodec/ac3dsp.h
index ec2f598451..ae33b361a9 100644
--- a/libavcodec/ac3dsp.h
+++ b/libavcodec/ac3dsp.h
@@ -22,6 +22,7 @@
 #ifndef AVCODEC_AC3DSP_H
 #define AVCODEC_AC3DSP_H
 
+#include <stddef.h>
 #include <stdint.h>
 
 /**