diff --git a/ChangeLog b/ChangeLog
index 889d480..1937d3c 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,7 @@
 2015-09-15  Niibe Yutaka  <gniibe@fsij.org>
 
+	* src/usb_stm32f103.c (std_set_interface): Bug fix for conf.
+
 	* src/gnuk.ld.in (__process3_stack_size__): Increase stack size of
 	GPG thread.
 	(__main_stack_size__): Decrease stack size of exception handlers.
diff --git a/src/usb_stm32f103.c b/src/usb_stm32f103.c
index c213d6a..ac96dda 100644
--- a/src/usb_stm32f103.c
+++ b/src/usb_stm32f103.c
@@ -727,7 +727,7 @@ static int std_set_interface (uint8_t req, struct control_info *detail)
 
   if ((req & REQUEST_DIR) == 1 || rcp != INTERFACE_RECIPIENT
       || detail->len != 0 || (detail->index >> 8) != 0
-      || (detail->value >> 8) != 0 || dev_p->current_configuration != 0)
+      || (detail->value >> 8) != 0 || dev_p->current_configuration == 0)
     return USB_UNSUPPORT;
 
   return usb_cb_interface (USB_SET_INTERFACE, detail);