diff --git a/fastboot/usb_windows.cpp b/fastboot/usb_windows.cpp
index 3dab5ac..0e5fba1 100644
--- a/fastboot/usb_windows.cpp
+++ b/fastboot/usb_windows.cpp
@@ -106,6 +106,7 @@
 
     if (nullptr == ret->adb_interface) {
         errno = GetLastError();
+        DBG("failed to open interface %S\n", interface_name);
         return nullptr;
     }
 
@@ -157,7 +158,7 @@
     unsigned count = 0;
     int ret;
 
-    DBG("usb_write %d\n", len);
+    DBG("usb_write %zu\n", len);
     if (nullptr != handle_) {
         // Perform write
         while(len > 0) {
@@ -195,7 +196,7 @@
     unsigned long read = 0;
     int ret;
 
-    DBG("usb_read %d\n", len);
+    DBG("usb_read %zu\n", len);
     if (nullptr != handle_) {
         while (1) {
             int xfer = (len > MAX_USBFS_BULK_SIZE) ? MAX_USBFS_BULK_SIZE : len;
@@ -269,19 +270,22 @@
         return 0;
 
     // Check vendor and product id first
-    if (!AdbGetUsbDeviceDescriptor(handle->adb_interface,
-                                 &device_desc)) {
+    if (!AdbGetUsbDeviceDescriptor(handle->adb_interface, &device_desc)) {
+        DBG("skipping device %x:%x\n", device_desc.idVendor, device_desc.idProduct);
         return 0;
     }
 
     // Then check interface properties
-    if (!AdbGetUsbInterfaceDescriptor(handle->adb_interface,
-                                    &interf_desc)) {
+    if (!AdbGetUsbInterfaceDescriptor(handle->adb_interface, &interf_desc)) {
+        DBG("skipping device %x:%x, failed to find interface\n", device_desc.idVendor,
+            device_desc.idProduct);
         return 0;
     }
 
     // Must have two endpoints
     if (2 != interf_desc.bNumEndpoints) {
+        DBG("skipping device %x:%x, incorrect number of endpoints\n", device_desc.idVendor,
+            device_desc.idProduct);
         return 0;
     }
 
@@ -305,9 +309,13 @@
     info.device_path[0] = 0;
 
     if (callback(&info) == 0) {
+        DBG("skipping device %x:%x, not selected by callback\n", device_desc.idVendor,
+            device_desc.idProduct);
         return 1;
     }
 
+    DBG("found device %x:%x (%s)\n", device_desc.idVendor, device_desc.idProduct,
+        info.serial_number);
     return 0;
 }
 
@@ -338,6 +346,7 @@
         }
         *copy_name = '\0';
 
+        DBG("attempting to open interface %S\n", next_interface->device_name);
         handle = do_usb_open(next_interface->device_name);
         if (NULL != handle) {
             // Lets see if this interface (device) belongs to us