thodg/libgit2

diff --git a/src/sha1_lookup.c b/src/sha1_lookup.c
index 8aca863..35149a1 100644
--- a/src/sha1_lookup.c
+++ b/src/sha1_lookup.c
@@ -183,9 +183,11 @@ int sha1_position(const void *table,
 			unsigned lo, unsigned hi,
 			const unsigned char *key)
 {
+	const unsigned char *base = table;
+
 	do {
 		unsigned mi = (lo + hi) / 2;
-		int cmp = git_oid__cmp(table + mi * stride, (git_oid *)key);
+		int cmp = git_oid__cmp((git_oid *)(base + mi * stride), (git_oid *)key);
 
 		if (!cmp)
 			return mi;