diff --git a/fs_mgr/liblp/builder.cpp b/fs_mgr/liblp/builder.cpp
index 7405039..54350a5 100644
--- a/fs_mgr/liblp/builder.cpp
+++ b/fs_mgr/liblp/builder.cpp
@@ -171,7 +171,8 @@
 std::unique_ptr<MetadataBuilder> MetadataBuilder::NewForUpdate(const IPartitionOpener& opener,
                                                                const std::string& source_partition,
                                                                uint32_t source_slot_number,
-                                                               uint32_t target_slot_number) {
+                                                               uint32_t target_slot_number,
+                                                               bool always_keep_source_slot) {
     auto metadata = ReadMetadata(opener, source_partition, source_slot_number);
     if (!metadata) {
         return nullptr;
@@ -189,7 +190,8 @@
         }
     }
 
-    if (IPropertyFetcher::GetInstance()->GetBoolProperty("ro.virtual_ab.enabled", false)) {
+    if (IPropertyFetcher::GetInstance()->GetBoolProperty("ro.virtual_ab.enabled", false) &&
+        !always_keep_source_slot) {
         if (!UpdateMetadataForInPlaceSnapshot(metadata.get(), source_slot_number,
                                               target_slot_number)) {
             return nullptr;
diff --git a/fs_mgr/liblp/include/liblp/builder.h b/fs_mgr/liblp/include/liblp/builder.h
index b43ccf0..1e9d636 100644
--- a/fs_mgr/liblp/include/liblp/builder.h
+++ b/fs_mgr/liblp/include/liblp/builder.h
@@ -209,10 +209,13 @@
     // metadata may not have the target slot's devices listed yet, in which
     // case, it is automatically upgraded to include all available block
     // devices.
+    // If |always_keep_source_slot| is set, on a Virtual A/B device, source slot
+    // partitions are kept. This is useful when applying a downgrade package.
     static std::unique_ptr<MetadataBuilder> NewForUpdate(const IPartitionOpener& opener,
                                                          const std::string& source_partition,
                                                          uint32_t source_slot_number,
-                                                         uint32_t target_slot_number);
+                                                         uint32_t target_slot_number,
+                                                         bool always_keep_source_slot = false);
 
     // Import an existing table for modification. If the table is not valid, for
     // example it contains duplicate partition names, then nullptr is returned.