diff --git a/constraints.txt b/constraints.txt
new file mode 100644
index 0000000..ae779a0
--- /dev/null
+++ b/constraints.txt
@@ -0,0 +1 @@
+cftime<1.1.1;python_version=='3.5'
\ No newline at end of file
diff --git a/requirements.txt b/requirements.txt
index 3a39688..56d054e 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,2 +1,3 @@
 --index-url https://pypi.python.org/simple/
+-c constraints.txt
 -e .