diff --git a/libavcodec/sonic.c b/libavcodec/sonic.c
index 31bbe46a44..3824c1f441 100644
--- a/libavcodec/sonic.c
+++ b/libavcodec/sonic.c
@@ -701,7 +701,7 @@ static int sonic_encode_frame(AVCodecContext *avctx, AVPacket *avpkt,
         }
 
         energy2 = sqrt(energy2/(s->channels*s->block_align));
-        energy1 = sqrt(2.0)*energy1/(s->channels*s->block_align);
+        energy1 = M_SQRT2*energy1/(s->channels*s->block_align);
 
         // increase bitrate when samples are like a gaussian distribution
         // reduce bitrate when samples are like a two-tailed exponential distribution