diff --git a/format_test.cc b/format_test.cc
index 0eb59261..fff02860 100644
--- a/format_test.cc
+++ b/format_test.cc
@@ -94,7 +94,7 @@ void Increment(char *s) {
 enum {BUFFER_SIZE = 256};
 
 #ifdef _MSC_VER
-# define vsnprintf _vsprintf_s
+# define vsnprintf vsprintf_s
 #endif
 
 void SPrintf(char *buffer, const char *format, ...) {