diff --git a/skeletons/OBJECT_IDENTIFIER.c b/skeletons/OBJECT_IDENTIFIER.c
index ffca36e..b2c97ae 100644
--- a/skeletons/OBJECT_IDENTIFIER.c
+++ b/skeletons/OBJECT_IDENTIFIER.c
@@ -80,7 +80,6 @@
 	return 0;
 }
 
-
 int
 OBJECT_IDENTIFIER_get_single_arc(const uint8_t *arcbuf, unsigned int arclen, signed int add, void *rvbufp, unsigned int rvsize) {
 	unsigned LE GCC_NOTUSED = 1; /* Little endian (x86) */
@@ -93,6 +92,8 @@
 	rvsize *= CHAR_BIT;	/* bytes to bits */
 	arclen *= 7;		/* bytes to bits */
 
+	assert(add <= 0);
+
 	/*
 	 * The arc has the number of bits
 	 * cannot be represented using supplied return value type.
@@ -133,11 +134,13 @@
 		/* Gather all bits into the accumulator */
 		for(accum = cache; arcbuf < arcend; arcbuf++)
 			accum = (accum << 7) | (*arcbuf & ~0x80);
-		if(accum < (unsigned)-add) {
+		if(accum < (unsigned)-add
+		|| accum > (ULONG_MAX-(unsigned long)(-add))) {
 			errno = ERANGE;	/* Overflow */
 			return -1;
 		}
-		*(unsigned long *)(void *)rvbuf = accum + add;	/* alignment OK! */
+		*(unsigned long *)(void *)rvbuf =
+			accum - (unsigned long)(-add); /* alignment OK! */
 		return 0;
 	}