diff --git a/client/async_file.cpp b/client/async_file.cpp
index fb19955288..c95a7bc905 100644
--- a/client/async_file.cpp
+++ b/client/async_file.cpp
@@ -29,6 +29,7 @@
 
 #ifdef _MSC_VER
 #define snprintf _snprintf
+#define tempnam _tempnam
 #endif
 
 #include "crypt.h"