diff --git a/nix/build-all.py b/nix/build-all.py
index 5844f44e2b..4fdfba5f8a 100644
--- a/nix/build-all.py
+++ b/nix/build-all.py
@@ -28,16 +28,19 @@
 #   if building with USE_OCCT additionally:                                   #
 #     * freetype * glx.h                                                      #
 #                                                                             #
+#   For python37 to install correctly additionally:                           #
+#     * libffi(-dev[el])                                                      #
+#                                                                             #
 #     on debian 7.8 these can be obtained with:                               #
 #          $ apt-get install git gcc g++ autoconf bison bzip2                 #
-#            libfreetype6-dev mesa-common-dev                                 #
+#            libfreetype6-dev mesa-common-dev libffi-dev                      #
 #                                                                             #
 #     on ubuntu 14.04:                                                        #
 #          $ apt-get install git gcc g++ autoconf bison make                  #
-#            libfreetype6-dev mesa-common-dev                                 #
+#            libfreetype6-dev mesa-common-dev libffi-dev                      #
 #                                                                             #
 #     on OS X El Capitan with homebrew:                                       #
-#          $ brew install git bison autoconf automake freetype                #
+#          $ brew install git bison autoconf automake freetype libffi         #
 #                                                                             #
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