diff --git a/sha1-lookup.c b/sha1-lookup.c
index 055dd87dc1..c4dc55d1f5 100644
--- a/sha1-lookup.c
+++ b/sha1-lookup.c
@@ -81,7 +81,7 @@ int sha1_pos(const unsigned char *sha1, void *table, size_t nr,
 				mi = (nr - 1) * (miv - lov) / (hiv - lov);
 				if (lo <= mi && mi < hi)
 					break;
-				die("oops");
+				die("BUG: assertion failed in binary search");
 			}
 		}
 		if (18 <= ofs)