diff --git a/constraints-legacy.txt b/constraints-legacy.txt
index ee888bc..6c96079 100644
--- a/constraints-legacy.txt
+++ b/constraints-legacy.txt
@@ -1,3 +1,4 @@
 # Oldest supported versions of major libraries can be added to this
 # file. They'll be tested with Python 2.7.
 pyrsistent==0.16.1
+jsonschema==3.2.0