diff --git a/src/fileio.c b/src/fileio.c
index b4a8e9a..20406bb 100644
--- a/src/fileio.c
+++ b/src/fileio.c
@@ -1122,7 +1122,7 @@
 	    if (!skip_read)
 	    {
 #if SIZEOF_INT > 2
-# ifdef __TANDEM
+# if defined(SSIZE_MAX) && (SSIZE_MAX < 0x10000L)
 		size = SSIZE_MAX;		    /* use max I/O size, 52K */
 # else
 		size = 0x10000L;		    /* use buffer >= 64K */