1 files changed, 1 insertions, 1 deletions
diff --git a/unsupported/test/FFTW.cpp b/unsupported/test/FFTW.cpp
index fdb41f2e0..c182cab9d 100644
--- a/unsupported/test/FFTW.cpp
+++ b/unsupported/test/FFTW.cpp
@@ -45,7 +45,7 @@ complex<long double>  promote(long double x) { return complex<long double>( x);
     {
         long double totalpower=0;
         long double difpower=0;
-        long double pi = acos(-1);
+        long double pi = acos((long double)-1 );
         cerr <<"idx\ttruth\t\tvalue\t|dif|=\n";
         for (size_t k0=0;k0<fftbuf.size();++k0) {
             complex<long double> acc = 0;