diff --git a/httplib.h b/httplib.h
index c69d8613d2..86c38aa820 100644
--- a/httplib.h
+++ b/httplib.h
@@ -205,7 +205,10 @@
 
 #pragma comment(lib, "ws2_32.lib")
 
+#ifndef _SSIZE_T_DEFINED
 using ssize_t = __int64;
+#define _SSIZE_T_DEFINED
+#endif
 #endif // _MSC_VER
 
 #ifndef S_ISREG