diff --git a/pocketfft_hdronly.h b/pocketfft_hdronly.h
index 7bf274f82fd1dc3bd5b693633e0a0fa54848fa0b..c0abd3714be6a16b2b57281133c52bdbbbf3dafd 100644
--- a/pocketfft_hdronly.h
+++ b/pocketfft_hdronly.h
@@ -270,7 +270,7 @@ template<typename T> class sincos_2pibyn
   {
   private:
     using Thigh = typename conditional<(sizeof(T)>sizeof(double)), T, double>::type;
-    size_t mask, shift;
+    size_t N, mask, shift;
     arr<cmplx<Thigh>> v1, v2;
 
     static cmplx<Thigh> calc(size_t x, size_t n, Thigh ang)
@@ -309,17 +309,19 @@ template<typename T> class sincos_2pibyn
 
   public:
     POCKETFFT_NOINLINE sincos_2pibyn(size_t n)
+      : N(n)
       {
       constexpr auto pi = 3.141592653589793238462643383279502884197L;
       Thigh ang = Thigh(0.25L*pi/n);
+      size_t nval = (n+2)/2;
       shift = 1;
-      while((size_t(1)<<shift)*(size_t(1)<<shift) < n) ++shift;
+      while((size_t(1)<<shift)*(size_t(1)<<shift) < nval) ++shift;
       mask = (size_t(1)<<shift)-1;
       v1.resize(mask+1);
       v1[0].Set(Thigh(1), Thigh(0));
       for (size_t i=1; i<v1.size(); ++i)
         v1[i]=calc(i,n,ang);
-      v2.resize((n+mask)/(mask+1));
+      v2.resize((nval+mask)/(mask+1));
       v2[0].Set(Thigh(1), Thigh(0));
       for (size_t i=1; i<v2.size(); ++i)
         v2[i]=calc(i*(mask+1),n,ang);
@@ -327,8 +329,14 @@ template<typename T> class sincos_2pibyn
 
     cmplx<T> operator[](size_t idx) const
       {
+      if (2*idx<=N)
+        {
+        auto x1=v1[idx&mask], x2=v2[idx>>shift];
+        return cmplx<T>(T(x1.r*x2.r-x1.i*x2.i), T(x1.r*x2.i+x1.i*x2.r));
+        }
+      idx = N-idx;
       auto x1=v1[idx&mask], x2=v2[idx>>shift];
-      return cmplx<T>(T(x1.r*x2.r-x1.i*x2.i), T(x1.r*x2.i+x1.i*x2.r));
+      return cmplx<T>(T(x1.r*x2.r-x1.i*x2.i), -T(x1.r*x2.i+x1.i*x2.r));
       }
   };
 
@@ -2484,10 +2492,9 @@ template<typename T0> class T_dcst23
     POCKETFFT_NOINLINE T_dcst23(size_t length)
       : fftplan(length), twiddle(length)
       {
-      constexpr auto pi = T0(3.141592653589793238462643383279502884197L);
-      const auto oo2n = pi*T0(0.5)/T0(length);
+      sincos_2pibyn<T0> tw(4*length);
       for (size_t i=0; i<length; ++i)
-        twiddle[i] = cos(oo2n*T0(i+1));
+        twiddle[i] = tw[i+1].r;
       }
 
     template<typename T> POCKETFFT_NOINLINE void exec(T c[], T0 fct, bool ortho,
@@ -2560,14 +2567,12 @@ template<typename T0> class T_dcst4
         rfft((N&1)? new pocketfft_r<T0>(N) : nullptr),
         C2((N&1) ? 0 : N/2)
       {
-      const auto oon = -T0(1.)/T0(N);
       if ((N&1)==0)
+        {
+        sincos_2pibyn<T0> tw(8*N);
         for (size_t i=0; i<N/2; ++i)
-          {
-          constexpr auto pi = T0(3.141592653589793238462643383279502884197L);
-          T0 ang = pi*oon*(T0(i)+T0(0.125));
-          C2[i].Set(cos(ang), sin(ang));
-          }
+          C2[i] = tw[8*N-8*i-1];
+        }
       }
 
     template<typename T> POCKETFFT_NOINLINE void exec(T c[], T0 fct,
diff --git a/stress.py b/stress.py
index f5e4ce276e63d605bbb7e3f87a2054d0591dc35e..635b351846794249e0394f6a321126d178557918 100644
--- a/stress.py
+++ b/stress.py
@@ -61,12 +61,12 @@ def test(err):
     b = fftn(ifftn(a.real, axes=axes, nthreads=nthreads), axes=axes, inorm=2,
              nthreads=nthreads)
     err = update_err(err, "cmax", _l2error(a.real, b, axes))
-    b = irfftn(rfftn(a.real, axes=axes, nthreads=nthreads), axes=axes, inorm=2,
-               lastsize=lastsize, nthreads=nthreads)
-    err = update_err(err, "rmax", _l2error(a.real, b, axes))
     b = ifftn(fftn(a.astype(np.complex64), axes=axes, nthreads=nthreads),
               axes=axes, inorm=2, nthreads=nthreads)
     err = update_err(err, "cmaxf", _l2error(a.astype(np.complex64), b, axes))
+    b = irfftn(rfftn(a.real, axes=axes, nthreads=nthreads), axes=axes, inorm=2,
+               lastsize=lastsize, nthreads=nthreads)
+    err = update_err(err, "rmax", _l2error(a.real, b, axes))
     b = irfftn(rfftn(a.real.astype(np.float32), axes=axes, nthreads=nthreads),
                axes=axes, inorm=2, lastsize=lastsize, nthreads=nthreads)
     err = update_err(err, "rmaxf", _l2error(a.real.astype(np.float32), b, axes))
@@ -113,6 +113,10 @@ def test(err):
         pypocketfft.dct(a_32.real, axes=axes, nthreads=nthreads, type=4),
         axes=axes, type=4, nthreads=nthreads, inorm=2)
     err = update_err(err, "c4maxf", _l2error(a_32.real, b, axes))
+    b = pypocketfft.dst(
+        pypocketfft.dst(a.real, axes=axes, nthreads=nthreads, type=1),
+        axes=axes, type=1, nthreads=nthreads, inorm=2)
+    err = update_err(err, "s1max", _l2error(a.real, b, axes))
     b = pypocketfft.dst(
         pypocketfft.dst(a_32.real, axes=axes, nthreads=nthreads, type=1),
         axes=axes, type=1, nthreads=nthreads, inorm=2)