diff --git a/src/session_win32_file_storage.cpp b/src/session_win32_file_storage.cpp
index ce3fba330..a5e54be84 100644
--- a/src/session_win32_file_storage.cpp
+++ b/src/session_win32_file_storage.cpp
@@ -186,7 +186,7 @@ void session_file_storage::save_to_file(HANDLE h,time_t timeout,std::string cons
 		int64_t timeout;
 		uint32_t crc;
 		uint32_t size;
-	} tmp = { timeout, 0, in.size() };
+	} tmp = { timeout, 0, static_cast<uint32_t>(in.size()) };
 	impl::crc32_calc crc_calc;
 	crc_calc.process_bytes(in.data(),in.size());
 	tmp.crc=crc_calc.checksum();