diff --git a/src/subscription.cr b/src/subscription.cr
index 1c0764a..e391360 100644
--- a/src/subscription.cr
+++ b/src/subscription.cr
@@ -34,8 +34,8 @@ struct Subscription
     @raw_last_checked = Time.utc.to_unix
   end
 
-  def in_range?(value : String, lowerbound : Int64?,
-                upperbound : Int64?) : Bool
+  private def in_range?(value : String, lowerbound : Int64?,
+                        upperbound : Int64?) : Bool
     lb = lowerbound.try &.to_f64
     ub = upperbound.try &.to_f64