diff --git a/lib/bcrypt/engine.rb b/lib/bcrypt/engine.rb
index 1a253b3..eb45c68 100644
--- a/lib/bcrypt/engine.rb
+++ b/lib/bcrypt/engine.rb
@@ -80,7 +80,9 @@ def self.hash_secret(secret, salt, _ = nil)
     # Generates a random salt with a given computational cost.
     def self.generate_salt(cost = self.cost)
       cost = cost.to_i
-      if cost > 0
+      if cost > MAX_COST
+        raise Errors::InvalidCost.new("cost must be <= #{MAX_COST}")
+      elsif cost > 0
         if cost < MIN_COST
           cost = MIN_COST
         end