diff --git a/requirements/core.txt b/requirements/core.txt
index 675903ec..24cad8d3 100644
--- a/requirements/core.txt
+++ b/requirements/core.txt
@@ -1,3 +1,4 @@
 jsonschema==3.2.0
+pyrsistent==0.14.0
 mmh3==2.5.1
 requests[security]>=2.9.1