diff --git a/lib/asn1/der_cmp.c b/lib/asn1/der_cmp.c
index 0a9c4ea76..306fcbdf5 100644
--- a/lib/asn1/der_cmp.c
+++ b/lib/asn1/der_cmp.c
@@ -60,10 +60,12 @@ heim_bit_string_cmp(const heim_bit_string *p, const heim_bit_string *q)
     i = memcmp(p->data, q->data, p->length / 8);
     if (i)
 	return i;
-    i = p->length / 8;
+    if ((p->length % 8) == 0)
+	return 0;
+    i = (p->length / 8);
     r1 = ((unsigned char *)p->data)[i];
     r2 = ((unsigned char *)q->data)[i];
-    i = 8 - p->length % 8;
+    i = 8 - (p->length % 8);
     r1 = r1 >> i;
     r2 = r2 >> i;
     return r1 - r2;