diff --git a/requirements_dev.txt b/requirements_dev.txt
index 9ab7b85226..f3cf11e38b 100644
--- a/requirements_dev.txt
+++ b/requirements_dev.txt
@@ -1,5 +1,5 @@
 # pinned dependencies for the development and CI environment
-appdirs==1.4.1
+appdirs
 args==0.1.0
 clint==0.5.1
 coverage==4.3.4
@@ -10,7 +10,7 @@ mccabe==0.6.1
 monotonic==1.2
 nose==1.3.7
 numpy==1.12.0
-packaging==16.8
+packaging
 pkginfo==1.4.1
 pluggy==0.4.0
 py==1.4.32
@@ -20,7 +20,7 @@ pyparsing==2.1.10
 requests==2.13.0
 requests-toolbelt==0.7.1
 setuptools-scm==1.15.0
-six==1.10.0
+six
 tox==2.6.0
 twine==1.8.1
 virtualenv==15.1.0