diff --git a/lang/cem/cpp.ansi/ch3bin.c b/lang/cem/cpp.ansi/ch3bin.c
index 3378e45f6..e85457e7a 100644
--- a/lang/cem/cpp.ansi/ch3bin.c
+++ b/lang/cem/cpp.ansi/ch3bin.c
@@ -8,7 +8,7 @@
 #include	"Lpars.h"
 #include	"arith.h"
 
-#define arith_sign (1 << (sizeof(arith)*8-1))
+#define arith_sign (1L << (sizeof(arith)*8-1))
 
 ch3bin(pval, pis_uns, oper, val, is_uns)
 	register arith *pval, val;