diff --git a/hgdriver/hgdev/hg_scanner_239.cpp b/hgdriver/hgdev/hg_scanner_239.cpp
index 0a866db..3f1c5f0 100644
--- a/hgdriver/hgdev/hg_scanner_239.cpp
+++ b/hgdriver/hgdev/hg_scanner_239.cpp
@@ -707,7 +707,7 @@ int hg_scanner_239::discard_all_images(void)
 				std::lock_guard<std::mutex>      lock(io_lock_);
 				ret = io_->read_interrupt(buf, &size);
 			}
-			while (ret == SCANNER_ERR_OK)
+			while (ret == SCANNER_ERR_OK && size)
 			{
 				pre_int++;
 				if (info->From == setting3399::IMG)
diff --git a/hgdriver/hgdev/hg_scanner_302.cpp b/hgdriver/hgdev/hg_scanner_302.cpp
index ff22dcd..11317eb 100644
--- a/hgdriver/hgdev/hg_scanner_302.cpp
+++ b/hgdriver/hgdev/hg_scanner_302.cpp
@@ -638,7 +638,7 @@ int hg_scanner_302::discard_all_images(void)
 		io_->set_timeout(100);
 		ret = io_->read_interrupt(buf, &size);
 	}
-	while (ret == SCANNER_ERR_OK)
+	while (ret == SCANNER_ERR_OK && size)
 	{
 		pre_int++;
 		if (info->From == setting3399::IMG)