diff --git a/lib/puma/configuration.rb b/lib/puma/configuration.rb
index 121e9c0c..c527db70 100644
--- a/lib/puma/configuration.rb
+++ b/lib/puma/configuration.rb
@@ -266,8 +266,10 @@ module Puma
       # requests and +max+ the maximum.
       #
       def threads(min, max)
+        min = Integer(min)
+        max = Integer(max)
         if min > max
-          raise "The minimum number of threads must be less than the max"
+          raise "The minimum (#{min}) number of threads must be less than the max (#{max})"
         end
 
         @options[:min_threads] = min