diff --git a/winsup/cygwin/include/cygwin/types.h b/winsup/cygwin/include/cygwin/types.h
index 0afa28509..9d810f5f4 100644
--- a/winsup/cygwin/include/cygwin/types.h
+++ b/winsup/cygwin/include/cygwin/types.h
@@ -101,7 +101,7 @@ typedef __ino32_t ino_t;
 
 #ifndef __key_t_defined
 #define __key_t_defined
-typedef long key_t;
+typedef long long key_t;
 #endif /* __key_t_defined */
 
 #ifndef __BIT_TYPES_DEFINED