diff --git a/math/s_ctanh.c b/math/s_ctanh.c
index fe38dae..31d7cfb 100644
--- a/math/s_ctanh.c
+++ b/math/s_ctanh.c
@@ -2,6 +2,7 @@
    Copyright (C) 1997, 2005 Free Software Foundation, Inc.
    This file is part of the GNU C Library.
    Contributed by Ulrich Drepper <address@hidden>, 1997.
+   Improvements by Judd Storrs and Jaroslav Hajek, 2010.
 
    The GNU C Library is free software; you can redistribute it and/or
    modify it under the terms of the GNU Lesser General Public
@@ -54,12 +55,20 @@ __ctanh (__complex__ double x)
     }
   else
     {
-      double sin2ix, cos2ix;
+      double sinix, cosix, sinhx, coshx;
       double den;
 
-      __sincos (2.0 * __imag__ x, &sin2ix, &cos2ix);
+      /*
+       *               sinh(a)*cosh(a) + i*sin(b)*cos(b)
+       * ctanh(a+bi) = ---------------------------------
+       *                      cos(b)^2 + sinh(a)^2
+       */
 
-      den = (__ieee754_cosh (2.0 * __real__ x) + cos2ix);
+      __sincos (__imag__ x, &sinix, &cosix);
+      sinhx = __ieee754_sinh (__real__ x);
+      coshx = __ieee754_cosh (__real__ x);
+
+      den = sinhx*sinhx + cosix*cosix;
 
       if (den == 0.0)
 	{
@@ -70,8 +79,8 @@ __ctanh (__complex__ double x)
 	}
       else
 	{
-	  __real__ res = __ieee754_sinh (2.0 * __real__ x) / den;
-	  __imag__ res = sin2ix / den;
+	  __real__ res = isfinite (den) ? sinhx * coshx / den : __copysign (1.0, __real__ x);
+	  __imag__ res = sinix * cosix / den;
 	}
     }
 
diff --git a/math/s_ctanhf.c b/math/s_ctanhf.c
index c331dba..fd3fbca 100644
--- a/math/s_ctanhf.c
+++ b/math/s_ctanhf.c
@@ -2,6 +2,7 @@
    Copyright (C) 1997, 2005 Free Software Foundation, Inc.
    This file is part of the GNU C Library.
    Contributed by Ulrich Drepper <address@hidden>, 1997.
+   Improvements by Judd Storrs and Jaroslav Hajek, 2010.
 
    The GNU C Library is free software; you can redistribute it and/or
    modify it under the terms of the GNU Lesser General Public
@@ -54,12 +55,20 @@ __ctanhf (__complex__ float x)
     }
   else
     {
-      float sin2ix, cos2ix;
+      float sinix, cosix, sinhx, coshx;
       float den;
 
-      __sincosf (2.0 * __imag__ x, &sin2ix, &cos2ix);
+      /*
+       *               sinh(a)*cosh(a) + i*sin(b)*cos(b)
+       * ctanh(a+bi) = ---------------------------------
+       *                      cos(b)^2 + sinh(a)^2
+       */
 
-      den = (__ieee754_coshf (2.0 * __real__ x) + cos2ix);
+      __sincosf (__imag__ x, &sinix, &cosix);
+      sinhx = __ieee754_sinhf (__real__ x);
+      coshx = __ieee754_coshf (__real__ x);
+
+      den = sinhx*sinhx + cosix*cosix;
 
       if (den == 0.0f)
 	{
@@ -70,8 +79,8 @@ __ctanhf (__complex__ float x)
 	}
       else
 	{
-	  __real__ res = __ieee754_sinhf (2.0 * __real__ x) / den;
-	  __imag__ res = sin2ix / den;
+	  __real__ res = isfinite (den) ? sinhx * coshx / den : __copysignf (1.0, __real__ x);
+	  __imag__ res = sinix * cosix / den;
 	}
     }
 
diff --git a/math/s_ctanhl.c b/math/s_ctanhl.c
index 77ca8f8..28bf458 100644
--- a/math/s_ctanhl.c
+++ b/math/s_ctanhl.c
@@ -2,6 +2,7 @@
    Copyright (C) 1997, 2005 Free Software Foundation, Inc.
    This file is part of the GNU C Library.
    Contributed by Ulrich Drepper <address@hidden>, 1997.
+   Improvements by Judd Storrs and Jaroslav Hajek, 2010.
 
    The GNU C Library is free software; you can redistribute it and/or
    modify it under the terms of the GNU Lesser General Public
@@ -54,12 +55,20 @@ __ctanhl (__complex__ long double x)
     }
   else
     {
-      long double sin2ix, cos2ix;
+      long double sinix, cosix, sinhx, coshx;
       long double den;
 
-      __sincosl (2.0 * __imag__ x, &sin2ix, &cos2ix);
+      /*
+       *               sinh(a)*cosh(a) + i*sin(b)*cos(b)
+       * ctanh(a+bi) = ---------------------------------
+       *                      cos(b)^2 + sinh(a)^2
+       */
 
-      den = (__ieee754_coshl (2.0 * __real__ x) + cos2ix);
+      __sincosl (__imag__ x, &sinix, &cosix);
+      sinhx = __ieee754_sinhl (__real__ x);
+      coshx = __ieee754_coshl (__real__ x);
+
+      den = sinhx*sinhx + cosix*cosix;
 
       if (den == 0.0L)
 	{
@@ -70,8 +79,8 @@ __ctanhl (__complex__ long double x)
 	}
       else
 	{
-	  __real__ res = __ieee754_sinhl (2.0 * __real__ x) / den;
-	  __imag__ res = sin2ix / den;
+	  __real__ res = isfinite (den) ? sinhx * coshx / den : __copysignl (1.0L, __real__ x);
+	  __imag__ res = sinix * cosix / den;
 	}
     }