diff --git a/net/appletalk/ddp.c b/net/appletalk/ddp.c
index 31fca64..b631cc7 100644
--- a/net/appletalk/ddp.c
+++ b/net/appletalk/ddp.c
@@ -922,13 +922,8 @@
 {
 	/* This ought to be unwrapped neatly. I'll trust gcc for now */
 	while (len--) {
-		sum += *data;
-		sum <<= 1;
-		if (sum & 0x10000) {
-			sum++;
-			sum &= 0xffff;
-		}
-		data++;
+		sum += *data++;
+		sum = rol16(sum, 1);
 	}
 	return sum;
 }