diff --git a/src/event.c b/src/event.c
index 88058c4e7..3bc0d635f 100644
--- a/src/event.c
+++ b/src/event.c
@@ -38,6 +38,10 @@
 
 #include <sys/types.h>
 
+#if !defined ssize_t && defined(_WIN32)
+    #define ssize_t ptrdiff_t
+#endif
+
 #define ssizeof(foo)            (ssize_t)sizeof(foo)
 #define countof(foo)            (ssizeof(foo) / ssizeof(foo[0]))