diff --git a/lib/puma/cli.rb b/lib/puma/cli.rb
index ace37038..48bd66ac 100644
--- a/lib/puma/cli.rb
+++ b/lib/puma/cli.rb
@@ -178,11 +178,11 @@ module Puma
         o.on '-t', '--threads INT', "min:max threads to use (default 0:16)" do |arg|
           min, max = arg.split(":")
           if max
-            @options[:min_threads] = min.to_i
-            @options[:max_threads] = max.to_i
+            @options[:min_threads] = min
+            @options[:max_threads] = max
           else
             @options[:min_threads] = 0
-            @options[:max_threads] = arg.to_i
+            @options[:max_threads] = arg
           end
         end
 
diff --git a/lib/puma/thread_pool.rb b/lib/puma/thread_pool.rb
index 3b686c32..843912b2 100644
--- a/lib/puma/thread_pool.rb
+++ b/lib/puma/thread_pool.rb
@@ -20,8 +20,8 @@ module Puma
       @spawned = 0
       @waiting = 0
 
-      @min = min
-      @max = max
+      @min = Integer(min)
+      @max = Integer(max)
       @block = block
       @extra = extra
 
@@ -34,7 +34,7 @@ module Puma
       @auto_trim = nil
 
       @mutex.synchronize do
-        min.times { spawn_thread }
+        @min.times { spawn_thread }
       end
     end
 
diff --git a/lib/rack/handler/puma.rb b/lib/rack/handler/puma.rb
index 55affbab..2193361d 100644
--- a/lib/rack/handler/puma.rb
+++ b/lib/rack/handler/puma.rb
@@ -31,8 +31,8 @@ module Rack
         puts "* Listening on tcp://#{options[:Host]}:#{options[:Port]}"
 
         server.add_tcp_listener options[:Host], options[:Port]
-        server.min_threads = Integer(min)
-        server.max_threads = Integer(max)
+        server.min_threads = min
+        server.max_threads = max
         yield server if block_given?
 
         begin
diff --git a/test/test_thread_pool.rb b/test/test_thread_pool.rb
index 7e6d0cc9..5fc203f8 100644
--- a/test/test_thread_pool.rb
+++ b/test/test_thread_pool.rb
@@ -32,6 +32,16 @@ class TestThreadPool < Test::Unit::TestCase
     assert_equal 1, pool.spawned
   end
 
+  def test_converts_pool_sizes
+    pool = new_pool('0', '1')
+
+    assert_equal 0, pool.spawned
+
+    pool << 1
+
+    assert_equal 1, pool.spawned
+  end
+
   def test_append_queues_on_max
     finish = false
     pool = new_pool(0, 1) { Thread.pass until finish }