diff --git a/thin-provisioning/thin_delta.cc b/thin-provisioning/thin_delta.cc
index 9d6337a..346d62c 100644
--- a/thin-provisioning/thin_delta.cc
+++ b/thin-provisioning/thin_delta.cc
@@ -498,11 +498,13 @@ namespace local {
 		while (ls.more_mappings()) {
 			auto &lm = ls.get_mapping();
 			e.left_only(lm.vbegin_, lm.dbegin_, lm.len_);
+			ls.consume(lm.len_);
 		}
 
 		while (rs.more_mappings()) {
 			auto &rm = rs.get_mapping();
 			e.right_only(rm.vbegin_, rm.dbegin_, rm.len_);
+			rs.consume(rm.len_);
 		}
 
 		e.complete();