diff --git a/main.cpp b/main.cpp
index a5e2602..0f05ee6 100644
--- a/main.cpp
+++ b/main.cpp
@@ -60,7 +60,7 @@ class thread_pool
 public:
 
     /* construction & destruction */
-    explicit thread_pool(unsigned int);
+    explicit thread_pool(size_t);
     ~thread_pool();
 
     /* disallowed operations */
@@ -93,10 +93,10 @@ public:
 
 };
 
-thread_pool::thread_pool(unsigned int thcount):
+thread_pool::thread_pool(size_t thcount):
         fin(false)
 {
-    for (int i = 0; i < thcount ; ++i)
+    for (size_t i = 0; i < thcount ; ++i)
         workers.emplace_back(&thread_pool::loop, this);
 }
 
@@ -174,7 +174,7 @@ void thread_pool::add_task(std::function<void()> func)
 
 void thread_pool::add_thread(size_t num = 1)
 {
-    for (int i = 0; i < num; ++i)
+    for (size_t i = 0; i < num; ++i)
     {
         workers.emplace_back(&thread_pool::loop, this);
     }