diff --git a/compress42.c b/compress42.c
index 4d33342..495bdf3 100644
--- a/compress42.c
+++ b/compress42.c
@@ -1373,7 +1373,7 @@ compress(fdin, fdout)
 		REG11	int			boff;
 		REG12	int			n_bits;
 		REG13	int			ratio;
-		REG14	long		checkpoint;
+		REG14	unsigned long long	checkpoint;
 		REG15	code_int	extcode;
 		union
 		{