diff --git a/dev-requirements.txt b/dev-requirements.txt
index a9665af3..a1b936a8 100644
--- a/dev-requirements.txt
+++ b/dev-requirements.txt
@@ -16,8 +16,8 @@
 # signatures.  The minimal install can only verify ed25519 signatures.  Pinned
 # packages: http://nvie.com/posts/pin-your-packages/
 cffi==1.11.2
-six=1.11.0
-iso8601=0.1.12
+six==1.11.0
+iso8601==0.1.12
 pynacl==1.2.1
 cryptography==2.1.4
 securesystemslib==0.10.8