diff --git a/doc/reference/c++/gf/gf_constructors.rst b/doc/reference/c++/gf/gf_constructors.rst
index 760cf1b6..57dfa2f4 100644
--- a/doc/reference/c++/gf/gf_constructors.rst
+++ b/doc/reference/c++/gf/gf_constructors.rst
@@ -45,7 +45,7 @@ There are more examples for each specializations in the corresponding pages.
     #include <triqs/gfs.hpp>
     using namespace triqs::gfs;
     int main(){
-     auto beta = 10;  
+     auto beta = 10.0;  
      gf<imfreq> gf {  {beta, Fermion}, {1,1}};
     }