diff --git a/requirements-dev.txt b/requirements-dev.txt
index 3ddeca7..1a6f3f0 100644
--- a/requirements-dev.txt
+++ b/requirements-dev.txt
@@ -3,10 +3,13 @@ atomicwrites==1.3.0
 attrs==19.1.0
 backcall==0.1.0
 decorator==4.4.0
-importlib-metadata==0.18
+entrypoints==0.3
+flake8==3.7.8
+importlib-metadata==0.19
 ipython-genutils==0.2.0
 ipython==7.7.0
 jedi==0.14.1
+mccabe==0.6.1
 more-itertools==7.2.0
 packaging==19.0
 parso==0.5.1
@@ -16,6 +19,8 @@ pluggy==0.12.0
 prompt-toolkit==2.0.9
 ptyprocess==0.6.0
 py==1.8.0
+pycodestyle==2.5.0
+pyflakes==2.1.1
 pygments==2.4.2
 pyparsing==2.4.1.1
 pytest==5.0.1
diff --git a/requirements.txt b/requirements.txt
index c568bfc..10848ba 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,4 +1,5 @@
 -i https://pypi.org/simple
+iso-639==0.4.5
 numpy==1.17.0
 pandas==0.25.0
 python-dateutil==2.8.0