diff --git a/src/lib/libast/sfio/sfmode.c b/src/lib/libast/sfio/sfmode.c
index 31c6a9b9a60c..78fade8ce06e 100644
--- a/src/lib/libast/sfio/sfmode.c
+++ b/src/lib/libast/sfio/sfmode.c
@@ -404,7 +404,7 @@ reg int		local;	/* a local call */
 
 	if(f->mode&SF_GETR)
 	{	f->mode &= ~SF_GETR;
-#ifdef MAP_TYPE
+#if defined(MAP_TYPE) && (_ptr_bits < 64)
 		if((f->bits&SF_MMAP) && (f->tiny[0] += 1) >= (4*SF_NMAP) )
 		{	/* turn off mmap to avoid page faulting */
 			sfsetbuf(f,(Void_t*)f->tiny,(size_t)SF_UNBOUND);