diff --git a/lower-constraints.txt b/lower-constraints.txt
index e9116638..d2a35574 100644
--- a/lower-constraints.txt
+++ b/lower-constraints.txt
@@ -12,6 +12,7 @@ future==0.16.0
 hacking==0.12.0
 imagesize==0.7.1
 iso8601==0.1.11
+isort==4.3.21
 Jinja2==2.10
 keystoneauth1==3.4.0
 linecache2==1.0.0
diff --git a/test-requirements.txt b/test-requirements.txt
index 7bc30fe2..692140d7 100644
--- a/test-requirements.txt
+++ b/test-requirements.txt
@@ -5,6 +5,7 @@
 hacking>=3.0.1,<3.1.0 # Apache-2.0
 
 coverage!=4.4,>=4.0 # Apache-2.0
+isort==4.3.21 # MIT
 python-subunit>=1.0.0 # Apache-2.0/BSD
 oslotest>=3.2.0 # Apache-2.0
 os-testr>=1.0.0 # Apache-2.0