diff --git a/Gemfile b/Gemfile
index aed4cdc..afa7ab6 100644
--- a/Gemfile
+++ b/Gemfile
@@ -13,4 +13,7 @@ end
 group :development do
   gem "rake", ">= 12.0"
   gem "rspec", ">= 3.4"
-end
\ No newline at end of file
+end
+
+# pin until we drop ruby 2.4 and then remove this entirely
+gem "parallel", "< 1.20"
\ No newline at end of file