diff --git a/README.md b/README.md
index f905555..106c9dd 100644
--- a/README.md
+++ b/README.md
@@ -6,6 +6,10 @@ Check the [blog post](https://guillaumegenthial.github.io/image-to-latex.html).
 
 ## Install
 
+**Python2 required.**
+
+Install python-dev for compiling multiprocessing (because this is a Python2 project), if Ubuntu just run `apt install python-dev`.
+
 Install pdflatex (latex to pdf) and ghostsript + [magick](https://www.imagemagick.org/script/install-source.php
 ) (pdf to png) on Linux
 
diff --git a/requirements.txt b/requirements.txt
index d14d654..54f25c4 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,10 +1,10 @@
-tensorflow
+tensorflow==1.15
 numpy
 scipy
-nltk
+nltk==3.2.5
 pillow
 distance
 logging
 multiprocessing
 six
-click
\ No newline at end of file
+click