diff --git a/README.md b/README.md
index 2d1340178480bf59420c67b3ccf9408af3e614b3..27fb76996003ece3a378c90bb284c48bb60e1957 100644
--- a/README.md
+++ b/README.md
@@ -15,7 +15,8 @@ Copyright Inria, please read the licence.
   - C++ compiler that supports
     - C++17 [compiler support list](http://en.cppreference.com/w/cpp/compiler_support)
     - [OpenMP](http://www.openmp.org/resources/openmp-compilers/)
-  - Custom BLAS, FFT implementations.
+  - Custom BLAS implementations (MKL, OpenBlas, ...)
+  - [FFTW3](https://www.fftw.org/) library.
 
 The following are optional:
 
diff --git a/include/scalfmm/tree/for_each.hpp b/include/scalfmm/tree/for_each.hpp
index 428f7b7783a1bf2a826f2cd614e76bfc4d61650d..52ff4e29e72da8f331b55c25262736a3eb73b5f5 100644
--- a/include/scalfmm/tree/for_each.hpp
+++ b/include/scalfmm/tree/for_each.hpp
@@ -7,6 +7,7 @@
 
 // #include <bits/utility.h>
 // #include <cstddef>
+#include <algorithm>
 #include <functional>
 #include <type_traits>
 #include <utility>