diff --git a/fs_mgr/libsnapshot/snapshot.cpp b/fs_mgr/libsnapshot/snapshot.cpp
index bd1e284..2c5bf75 100644
--- a/fs_mgr/libsnapshot/snapshot.cpp
+++ b/fs_mgr/libsnapshot/snapshot.cpp
@@ -1619,6 +1619,18 @@
         //    as dm-snapshot (for example, after merge completes).
         bool should_unmap = current_slot != Slot::Target;
         bool should_delete = ShouldDeleteSnapshot(flashing_status, current_slot, name);
+        if (should_unmap && android::base::EndsWith(name, device_->GetSlotSuffix())) {
+            // Something very unexpected has happened - we want to unmap this
+            // snapshot, but it's on the wrong slot. We can't unmap an active
+            // partition. If this is not really a snapshot, skip the unmap
+            // step.
+            auto& dm = DeviceMapper::Instance();
+            if (dm.GetState(name) == DmDeviceState::INVALID || !IsSnapshotDevice(name)) {
+                LOG(ERROR) << "Detected snapshot " << name << " on " << current_slot << " slot"
+                           << " for source partition; removing without unmap.";
+                should_unmap = false;
+            }
+        }
 
         bool partition_ok = true;
         if (should_unmap && !UnmapPartitionWithSnapshot(lock, name)) {
diff --git a/fs_mgr/libsnapshot/snapshot_test.cpp b/fs_mgr/libsnapshot/snapshot_test.cpp
index 25500b5..6ed0129 100644
--- a/fs_mgr/libsnapshot/snapshot_test.cpp
+++ b/fs_mgr/libsnapshot/snapshot_test.cpp
@@ -2021,6 +2021,34 @@
     ASSERT_TRUE(IsPartitionUnchanged("sys_b"));
 }
 
+TEST_F(SnapshotUpdateTest, CancelOnTargetSlot) {
+    AddOperationForPartitions();
+
+    // Execute the update from B->A.
+    test_device->set_slot_suffix("_b");
+    ASSERT_TRUE(sm->BeginUpdate());
+    ASSERT_TRUE(sm->CreateUpdateSnapshots(manifest_));
+
+    std::string path;
+    ASSERT_TRUE(CreateLogicalPartition(
+            CreateLogicalPartitionParams{
+                    .block_device = fake_super,
+                    .metadata_slot = 0,
+                    .partition_name = "sys_a",
+                    .timeout_ms = 1s,
+                    .partition_opener = opener_.get(),
+            },
+            &path));
+
+    // Hold sys_a open so it can't be unmapped.
+    unique_fd fd(open(path.c_str(), O_RDONLY));
+
+    // Switch back to "A", make sure we can cancel. Instead of unmapping sys_a
+    // we should simply delete the old snapshots.
+    test_device->set_slot_suffix("_a");
+    ASSERT_TRUE(sm->BeginUpdate());
+}
+
 class FlashAfterUpdateTest : public SnapshotUpdateTest,
                              public WithParamInterface<std::tuple<uint32_t, bool>> {
   public: