diff --git a/apps/codecs/lib/mdct.c b/apps/codecs/lib/mdct.c
index 03baa4db4a..3c9fe41f20 100644
--- a/apps/codecs/lib/mdct.c
+++ b/apps/codecs/lib/mdct.c
@@ -139,10 +139,10 @@ void ff_imdct_half(unsigned int nbits, fixed32 *output, const fixed32 *input)
                 fixed32 r0,i0,r1,i1;
                 XNPROD31_R(z1[1], z1[0], T[0], T[1], r0, i1 ); T+=newstep;
                 XNPROD31_R(z2[1], z2[0], T[1], T[0], r1, i0 ); T+=newstep;
-                z1[0] = r0;
-                z1[1] = i0;
-                z2[0] = r1;
-                z2[1] = i1;
+                z1[0] = -r0;
+                z1[1] = -i0;
+                z2[0] = -r1;
+                z2[1] = -i1;
                 z1+=2;
                 z2-=2;
             }
@@ -171,10 +171,10 @@ void ff_imdct_half(unsigned int nbits, fixed32 *output, const fixed32 *input)
                 v0 += (t0 = (T[0]>>1));
                 v1 += (t1 = (T[1]>>1));
                 XNPROD31_R(z2[1], z2[0], v1, v0, r1, i0 );
-                z1[0] = r0;
-                z1[1] = i0;
-                z2[0] = r1;
-                z2[1] = i1;
+                z1[0] = -r0;
+                z1[1] = -i0;
+                z2[0] = -r1;
+                z2[1] = -i1;
                 z1+=2;
                 z2-=2;
                 V+=2;
@@ -205,10 +205,10 @@ void ff_imdct_half(unsigned int nbits, fixed32 *output, const fixed32 *input)
                 t0 = v0-q0;
                 t1 = v1-q1;
                 XNPROD31_R(z2[1], z2[0], t1, t0, r1, i0 );
-                z1[0] = r0;
-                z1[1] = i0;
-                z2[0] = r1;
-                z2[1] = i1;
+                z1[0] = -r0;
+                z1[1] = -i0;
+                z2[0] = -r1;
+                z2[1] = -i1;
                 z1+=2;
                 z2-=2;
                 T+=2;
@@ -220,10 +220,10 @@ void ff_imdct_half(unsigned int nbits, fixed32 *output, const fixed32 *input)
                 v0 = t0-q0;
                 v1 = t1-q1;
                 XNPROD31_R(z2[1], z2[0], v1, v0, r1, i0 );
-                z1[0] = r0;
-                z1[1] = i0;
-                z2[0] = r1;
-                z2[1] = i1;
+                z1[0] = -r0;
+                z1[1] = -i0;
+                z2[0] = -r1;
+                z2[1] = -i1;
                 z1+=2;
                 z2-=2;
                 V+=2;