diff --git a/encoder/ratecontrol.c b/encoder/ratecontrol.c
index 9e0c8a4372240a6103f655808493ca1b51eb7d05..e2ce4d49d65b34480b347909f97a115b3bffa10d 100644
--- a/encoder/ratecontrol.c
+++ b/encoder/ratecontrol.c
@@ -35,6 +35,10 @@
 
 #define DEBUG_RC 0
 
+#ifdef SYS_MACOSX
+#define exp2f(x) ( (float) exp2( (x) ) )
+#endif
+
 struct x264_ratecontrol_t
 {
     /* constants */