diff --git a/libavcodec/x264.c b/libavcodec/x264.c
index 0e850f5739..df5df9810a 100644
--- a/libavcodec/x264.c
+++ b/libavcodec/x264.c
@@ -19,6 +19,7 @@
 
 #include "avcodec.h"
 #include <x264.h>
+#include <math.h>
 
 typedef struct X264Context {
     x264_param_t params;