diff --git a/libbuild2-autoconf/libbuild2/autoconf/checks/ssize_t.h b/libbuild2-autoconf/libbuild2/autoconf/checks/ssize_t.h
new file mode 100644
index 0000000..16dcd18
--- /dev/null
+++ b/libbuild2-autoconf/libbuild2/autoconf/checks/ssize_t.h
@@ -0,0 +1,27 @@
+// ssize_t : BUILD2_AUTOCONF_LIBC_VERSION
+
+#ifndef BUILD2_AUTOCONF_LIBC_VERSION
+#  error BUILD2_AUTOCONF_LIBC_VERSION appears to be conditionally included
+#endif
+
+#undef ssize_t
+
+/* POSIX and MinGW (which also has <sys/types.h> that defines ssize_t).
+ */
+#if defined(__linux__)                  || \
+    defined(__FreeBSD__)                || \
+    defined(__OpenBSD__)                || \
+    defined(__NetBSD__)                 || \
+    defined(BUILD2_AUTOCONF_MACOS)      || \
+    defined(__MINGW32__)                || \
+    (defined(__sun) && defined(__SVR4)) || \
+    defined(__CYGWIN__)
+#  include <sys/types.h>
+   /* If available, we do nothing. */
+#elif defined(_WIN32)
+#  include <basetsd.h>
+   typedef SSIZE_T ssize_t;
+#else
+   /* Else define it to int (suggested fallback by libevent). */
+#   define ssize_t int
+#endif