diff --git a/third_party/leveldatabase/port/port_chromium.h b/third_party/leveldatabase/port/port_chromium.h
index a7c449eba19c..acbce7efd582 100644
--- a/third_party/leveldatabase/port/port_chromium.h
+++ b/third_party/leveldatabase/port/port_chromium.h
@@ -26,7 +26,11 @@
 #endif
 
 #if defined(OS_WIN)
+#  if !defined(_SSIZE_T_) && !defined(_SSIZE_T_DEFINED)
 typedef SSIZE_T ssize_t;
+#  define _SSIZE_T_
+#  define _SSIZE_T_DEFINED
+#  endif
 #endif
 
 namespace leveldb {