diff --git a/vendor/github.com/google/btree/btree.go b/vendor/github.com/google/btree/btree.go
index b83acdb..6f5184f 100644
--- a/vendor/github.com/google/btree/btree.go
+++ b/vendor/github.com/google/btree/btree.go
@@ -12,6 +12,9 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+//go:build !go1.18
+// +build !go1.18
+
 // Package btree implements in-memory B-Trees of arbitrary degree.
 //
 // btree implements an in-memory B-Tree for use as an ordered data structure.
@@ -476,7 +479,7 @@
 		child := n.mutableChild(i)
 		// merge with right child
 		mergeItem := n.items.removeAt(i)
-		mergeChild := n.children.removeAt(i + 1)
+		mergeChild := n.children.removeAt(i + 1).mutableFor(n.cow)
 		child.items = append(child.items, mergeItem)
 		child.items = append(child.items, mergeChild.items...)
 		child.children = append(child.children, mergeChild.children...)