diff --git a/src/hashids.c b/src/hashids.c
index 7f0b2f3..8d68509 100644
--- a/src/hashids.c
+++ b/src/hashids.c
@@ -6,6 +6,13 @@
 
 #include "hashids.h"
 
+#ifdef _MSC_VER
+#include <BaseTsd.h>
+typedef SSIZE_T ssize_t;
+#else
+#include <unistd.h>
+#endif
+
 /* branch prediction hinting */
 #ifndef __has_builtin
 #   define __has_builtin(x) (0)