diff -rup boost_1_48_0.orig/boost/math/complex/acosh.hpp boost_1_48_0/boost/math/complex/acosh.hpp
--- boost_1_48_0.orig/boost/math/complex/acosh.hpp	2005-10-15 13:59:11.000000000 +0200
+++ boost_1_48_0/boost/math/complex/acosh.hpp	2011-11-24 09:28:19.920274990 +0100
@@ -24,7 +24,7 @@ inline std::complex<T> acosh(const std::
    // as well as compatibility with C99.
    //
    std::complex<T> result = boost::math::acos(z);
-   if(!detail::test_is_nan(result.imag()) && result.imag() <= 0)
+   if(!signbit(z.imag()))
       return detail::mult_i(result);
    return detail::mult_minus_i(result);
 }
diff -rup boost_1_48_0.orig/boost/math/complex/acos.hpp boost_1_48_0/boost/math/complex/acos.hpp
--- boost_1_48_0.orig/boost/math/complex/acos.hpp	2006-07-24 23:33:20.000000000 +0200
+++ boost_1_48_0/boost/math/complex/acos.hpp	2011-11-24 09:02:13.426657171 +0100
@@ -11,6 +11,7 @@
 #ifndef BOOST_MATH_LOG1P_INCLUDED
 #  include <boost/math/special_functions/log1p.hpp>
 #endif
+#include <boost/math/special_functions/sign.hpp>
 #include <boost/assert.hpp>
 
 #ifdef BOOST_NO_STDC_NAMESPACE
@@ -222,9 +223,9 @@ std::complex<T> acos(const std::complex<
    //
    // Finish off by working out the sign of the result:
    //
-   if(z.real() < 0)
+   if(signbit(z.real()))
       real = s_pi - real;
-   if(z.imag() > 0)
+   if(!signbit(z.imag()))
       imag = -imag;
 
    return std::complex<T>(real, imag);
diff -rup boost_1_48_0.orig/boost/math/complex/asin.hpp boost_1_48_0/boost/math/complex/asin.hpp
--- boost_1_48_0.orig/boost/math/complex/asin.hpp	2006-07-24 23:38:40.000000000 +0200
+++ boost_1_48_0/boost/math/complex/asin.hpp	2011-11-24 08:56:33.772109729 +0100
@@ -11,6 +11,7 @@
 #ifndef BOOST_MATH_LOG1P_INCLUDED
 #  include <boost/math/special_functions/log1p.hpp>
 #endif
+#include <boost/math/special_functions/sign.hpp>
 #include <boost/assert.hpp>
 
 #ifdef BOOST_NO_STDC_NAMESPACE
@@ -232,9 +233,9 @@ inline std::complex<T> asin(const std::c
    //
    // Finish off by working out the sign of the result:
    //
-   if(z.real() < 0)
+   if(signbit(z.real()))
       real = -real;
-   if(z.imag() < 0)
+   if(signbit(z.imag()))
       imag = -imag;
 
    return std::complex<T>(real, imag);
diff -rup boost_1_48_0.orig/boost/math/complex/atanh.hpp boost_1_48_0/boost/math/complex/atanh.hpp
--- boost_1_48_0.orig/boost/math/complex/atanh.hpp	2005-12-16 15:10:05.000000000 +0100
+++ boost_1_48_0/boost/math/complex/atanh.hpp	2011-11-24 09:04:14.096107285 +0100
@@ -12,6 +12,7 @@
 #ifndef BOOST_MATH_LOG1P_INCLUDED
 #  include <boost/math/special_functions/log1p.hpp>
 #endif
+#include <boost/math/special_functions/sign.hpp>
 #include <boost/assert.hpp>
 
 #ifdef BOOST_NO_STDC_NAMESPACE
@@ -194,7 +195,7 @@ std::complex<T> atanh(const std::complex
       }
       
       real /= four;
-      if(z.real() < 0)
+      if(signbit(z.real()))
          real = -real;
 
       //
@@ -234,7 +235,7 @@ std::complex<T> atanh(const std::complex
             imag = std::atan2(two*y, 1 - x*x);
       }
       imag /= two;
-      if(z.imag() < 0)
+      if(signbit(z.imag()))
          imag = -imag;
    }
    return std::complex<T>(real, imag);