diff --git a/include/complex b/include/complex
index d553dad..95be60c 100644
--- a/include/complex
+++ b/include/complex
@@ -1341,7 +1341,8 @@ _LIBCPP_HIDE_FROM_ABI complex<_Tp> acos(const complex<_Tp>& __x) {
   }
   if (std::__constexpr_isinf(__x.imag()))
     return complex<_Tp>(__pi / _Tp(2), -__x.imag());
-  if (__x.real() == 0 && (__x.imag() == 0 || std::isnan(__x.imag())))
+  // Somehow isnan can be a macro, so we use __constexpr_isnan
+  if (__x.real() == 0 && (__x.imag() == 0 || std::__constexpr_isnan(__x.imag())))
     return complex<_Tp>(__pi / _Tp(2), -__x.imag());
   complex<_Tp> __z = std::log(__x + std::sqrt(std::__sqr(__x) - _Tp(1)));
   if (std::signbit(__x.imag()))