diff --git a/lib/mock_redis/database.rb b/lib/mock_redis/database.rb
index 13deb73..4691313 100644
--- a/lib/mock_redis/database.rb
+++ b/lib/mock_redis/database.rb
@@ -267,6 +267,8 @@ def type(key)
         'set'
       elsif zsety?(key)
         'zset'
+      elsif streamy?(key)
+        'stream'
       else
         raise ArgumentError, "Not sure how #{data[key].inspect} got in here"
       end