diff --git a/libavcodec/dsputil.h b/libavcodec/dsputil.h
index 3656d1c3b5..50889bb1d1 100644
--- a/libavcodec/dsputil.h
+++ b/libavcodec/dsputil.h
@@ -840,7 +840,7 @@ typedef struct {
     int sign_convention;
 
     /* pre/post rotation tables */
-    FFTSample *tcos;
+    const FFTSample *tcos;
     FFTSample *tsin;
     FFTContext fft;
 } RDFTContext;
diff --git a/libavcodec/rdft.c b/libavcodec/rdft.c
index 0fe26ab01a..ed4e39aa08 100644
--- a/libavcodec/rdft.c
+++ b/libavcodec/rdft.c
@@ -64,7 +64,6 @@ av_cold int ff_rdft_init(RDFTContext *s, int nbits, enum RDFTransformType trans)
     s->tcos = ff_cos_tabs[nbits-4];
     s->tsin = ff_sin_tabs[nbits-4]+(trans == RDFT || trans == IRIDFT)*(n>>2);
     for (i = 0; i < (n>>2); i++) {
-        s->tcos[i] = cos(i*theta);
         s->tsin[i] = sin(i*theta);
     }
     return 0;