diff --git a/tools/hello.cpp b/tools/hello.cpp
index 0c6639a..3012d94 100644
--- a/tools/hello.cpp
+++ b/tools/hello.cpp
@@ -355,13 +355,13 @@ main (void)
     auto queues = pdevice.queue_families ();
     int graphics_queue_id = -1, present_queue_id = -1;
 
-    for (int i = 0, last = queues.size (); i != last; ++i)
+    for (size_t i = 0, last = queues.size (); i != last; ++i)
         if (queues[i].queueCount > 0 && queues[i].queueFlags & VK_QUEUE_GRAPHICS_BIT) {
             graphics_queue_id = i;
             break;
         }
 
-    for (int i = 0, last = queues.size (); i != last; ++i) {
+    for (size_t i = 0, last = queues.size (); i != last; ++i) {
         if (cruft::vk::error::try_query (vkGetPhysicalDeviceSurfaceSupportKHR,
                                          pdevice.native (), i, surface)) {
             present_queue_id = i;