diff --git a/source/ftl/map.c b/source/ftl/map.c
index af59e45..8778d91 100644
--- a/source/ftl/map.c
+++ b/source/ftl/map.c
@@ -264,6 +264,9 @@ static uint32_t find_last_group(struct ftl_map *map, uint32_t block)
 	uint32_t ngroups = UINT32_C(1) << map->log2_groups_per_block;
 	uint32_t mid, low = 0, high = ngroups - 1;
 
+	low += block << map->log2_groups_per_block;
+	high += block << map->log2_groups_per_block;
+
 	while (low <= high) {
 		mid = (low + high) / 2;
 
@@ -272,9 +275,8 @@ static uint32_t find_last_group(struct ftl_map *map, uint32_t block)
 			continue;
 		}
 
-		if (((mid + 1) >= ngroups) ||
-		    is_group_erased(map, mid + 1))
-			return (block << map->log2_groups_per_block) + mid;
+		if (is_group_erased(map, mid + 1))
+			return mid;
 
 		low = mid + 1;
 	}