diff --git a/drivers/md/bcache/bset.h b/drivers/md/bcache/bset.h
index e67386001814..bc9975526aa1 100644
--- a/drivers/md/bcache/bset.h
+++ b/drivers/md/bcache/bset.h
@@ -353,12 +353,30 @@ void bch_bset_fix_lookup_table(struct btree *, struct bkey *);
 struct bkey *__bch_bset_search(struct btree *, struct bset_tree *,
 			   const struct bkey *);
 
+/*
+ * Returns the first key that is strictly greater than search
+ */
 static inline struct bkey *bch_bset_search(struct btree *b, struct bset_tree *t,
 					   const struct bkey *search)
 {
 	return search ? __bch_bset_search(b, t, search) : t->data->start;
 }
 
+#define PRECEDING_KEY(_k)					\
+({								\
+	struct bkey *_ret = NULL;				\
+								\
+	if (KEY_INODE(_k) || KEY_OFFSET(_k)) {			\
+		_ret = &KEY(KEY_INODE(_k), KEY_OFFSET(_k), 0);	\
+								\
+		if (!_ret->low)					\
+			_ret->high--;				\
+		_ret->low--;					\
+	}							\
+								\
+	_ret;							\
+})
+
 bool bch_bkey_try_merge(struct btree *, struct bkey *, struct bkey *);
 void bch_btree_sort_lazy(struct btree *);
 void bch_btree_sort_into(struct btree *, struct btree *);
diff --git a/drivers/md/bcache/btree.c b/drivers/md/bcache/btree.c
index 7dff73ba1b71..773b0e929ff4 100644
--- a/drivers/md/bcache/btree.c
+++ b/drivers/md/bcache/btree.c
@@ -1844,19 +1844,14 @@ static bool btree_insert_key(struct btree *b, struct btree_op *op,
 
 	if (!b->level) {
 		struct btree_iter iter;
-		struct bkey search = KEY(KEY_INODE(k), KEY_START(k), 0);
 
 		/*
 		 * bset_search() returns the first key that is strictly greater
 		 * than the search key - but for back merging, we want to find
-		 * the first key that is greater than or equal to KEY_START(k) -
-		 * unless KEY_START(k) is 0.
+		 * the previous key.
 		 */
-		if (KEY_OFFSET(&search))
-			SET_KEY_OFFSET(&search, KEY_OFFSET(&search) - 1);
-
 		prev = NULL;
-		m = bch_btree_iter_init(b, &iter, &search);
+		m = bch_btree_iter_init(b, &iter, PRECEDING_KEY(&START_KEY(k)));
 
 		if (fix_overlapping_extents(b, k, &iter, replace_key)) {
 			op->insert_collision = true;