diff --git a/lib/capnp_c.h b/lib/capnp_c.h
index db8f92e..2b4b22a 100644
--- a/lib/capnp_c.h
+++ b/lib/capnp_c.h
@@ -27,7 +27,8 @@
  * Windows seems to only have SSIZE_T in BaseTsd.h
  */
 #ifdef _MSC_VER
-typedef intmax_t ssize_t;
+#include <BaseTsd.h>
+typedef SSIZE_T ssize_t;
 #else
 #include <stddef.h>
 #endif