diff --git a/caching/cache_check.cc b/caching/cache_check.cc
index cbe4581..419169f 100644
--- a/caching/cache_check.cc
+++ b/caching/cache_check.cc
@@ -254,7 +254,7 @@ namespace {
 				out << "examining discard bitset" << end_message();
 				{
 					nested_output::nest _ = out.push();
-					bitset discards(tm, sb.discard_root, sb.discard_nr_blocks);
+					persistent_data::bitset discards(tm, sb.discard_root, sb.discard_nr_blocks);
 				}
 			}
 		}
diff --git a/caching/cache_repair.cc b/caching/cache_repair.cc
index 5d1aafa..4a8cd9c 100644
--- a/caching/cache_repair.cc
+++ b/caching/cache_repair.cc
@@ -23,7 +23,7 @@ namespace {
 	emitter::ptr output_emitter(string const &path) {
 		block_manager<>::ptr bm = open_bm(path, block_io<>::READ_WRITE);
 		metadata::ptr md(new metadata(bm, metadata::CREATE));
-		return create_restore_emitter(md);
+		return create_restore_emitter(md, true);
 	}
 
 	int repair(string const &old_path, string const &new_path) {
diff --git a/caching/cache_restore.cc b/caching/cache_restore.cc
index b672932..536ef82 100644
--- a/caching/cache_restore.cc
+++ b/caching/cache_restore.cc
@@ -23,20 +23,23 @@ namespace {
 	struct flags {
 		flags()
 			: metadata_version(1),
-			  override_metadata_version(false) {
+			  override_metadata_version(false),
+			  clean_shutdown(true) {
 		}
 
 		optional<string> input;
 		optional<string> output;
+
 		uint32_t metadata_version;
 		bool override_metadata_version;
+		bool clean_shutdown;
 	};
 
 	int restore(flags const &fs) {
 		try {
 			block_manager<>::ptr bm = open_bm(*fs.output, block_io<>::READ_WRITE);
 			metadata::ptr md(new metadata(bm, metadata::CREATE));
-			emitter::ptr restorer = create_restore_emitter(md);
+			emitter::ptr restorer = create_restore_emitter(md, fs.clean_shutdown);
 
 			if (fs.override_metadata_version) {
 				cerr << "overriding" << endl;
@@ -63,7 +66,8 @@ namespace {
 		    << "  {-o|--output} <output device or file>" << endl
 		    << "  {-V|--version}" << endl
 		    << endl
-		    << "  {--debug-override-metadata-version} <integer>" << endl;
+		    << "  {--debug-override-metadata-version} <integer>" << endl
+		    << "  {--omit-clean-shutdown}" << endl;
 
 	}
 }
@@ -76,6 +80,7 @@ int main(int argc, char **argv)
 	char const *short_opts = "hi:o:V";
 	option const long_opts[] = {
 		{ "debug-override-metadata-version", required_argument, NULL, 0 },
+		{ "omit-clean-shutdown", no_argument, NULL, 1 },
 		{ "help", no_argument, NULL, 'h'},
 		{ "input", required_argument, NULL, 'i' },
 		{ "output", required_argument, NULL, 'o'},
@@ -90,6 +95,10 @@ int main(int argc, char **argv)
 			fs.override_metadata_version = true;
 			break;
 
+		case 1:
+			fs.clean_shutdown = false;
+			break;
+
 		case 'h':
 			usage(cout, prog_name);
 			return 0;
diff --git a/caching/metadata.cc b/caching/metadata.cc
index 2d8ef83..0a246f9 100644
--- a/caching/metadata.cc
+++ b/caching/metadata.cc
@@ -47,13 +47,13 @@ metadata::metadata(block_manager<>::ptr bm, open_type ot)
 }
 
 void
-metadata::commit()
+metadata::commit(bool clean_shutdown)
 {
 	commit_space_map();
 	commit_mappings();
 	commit_hints();
 	commit_discard_bits();
-	commit_superblock();
+	commit_superblock(clean_shutdown);
 }
 
 void
@@ -79,7 +79,7 @@ metadata::create_metadata(block_manager<>::ptr bm)
 	// We can't instantiate the hint array yet, since we don't know the
 	// hint width.
 
-	discard_bits_ = bitset::ptr(new bitset(tm_));
+	discard_bits_ = persistent_data::bitset::ptr(new persistent_data::bitset(tm_));
 }
 
 void
@@ -100,8 +100,8 @@ metadata::open_metadata(block_manager<>::ptr bm)
 				       sb_.hint_root, sb_.cache_blocks));
 
 	if (sb_.discard_root)
-		discard_bits_ = bitset::ptr(
-			new bitset(tm_, sb_.discard_root, sb_.discard_nr_blocks));
+		discard_bits_ = persistent_data::bitset::ptr(
+			new persistent_data::bitset(tm_, sb_.discard_root, sb_.discard_nr_blocks));
 }
 
 void
@@ -130,10 +130,13 @@ metadata::commit_discard_bits()
 }
 
 void
-metadata::commit_superblock()
+metadata::commit_superblock(bool clean_shutdown)
 {
-	sb_.flags.set_flag(superblock_flags::CLEAN_SHUTDOWN);
+	if (clean_shutdown)
+		sb_.flags.set_flag(superblock_flags::CLEAN_SHUTDOWN);
+
 	write_superblock(tm_->get_bm(), sb_);
+
 	sb_.flags.clear_flag(superblock_flags::CLEAN_SHUTDOWN);
 }
 
diff --git a/caching/metadata.h b/caching/metadata.h
index a606878..46c2b93 100644
--- a/caching/metadata.h
+++ b/caching/metadata.h
@@ -29,7 +29,7 @@ namespace caching {
 
 		metadata(block_manager<>::ptr bm, open_type ot);
 
-		void commit();
+		void commit(bool clean_shutdown = true);
 		void setup_hint_array(size_t width);
 
 
@@ -39,7 +39,7 @@ namespace caching {
 		checked_space_map::ptr metadata_sm_;
 		mapping_array::ptr mappings_;
 		hint_array::ptr hints_;
-		bitset::ptr discard_bits_;
+		persistent_data::bitset::ptr discard_bits_;
 
 	private:
 		void init_superblock();
@@ -51,7 +51,7 @@ namespace caching {
 		void commit_mappings();
 		void commit_hints();
 		void commit_discard_bits();
-		void commit_superblock();
+		void commit_superblock(bool clean_shutdown);
 	};
 };
 
diff --git a/caching/restore_emitter.cc b/caching/restore_emitter.cc
index 6c862bf..55be343 100644
--- a/caching/restore_emitter.cc
+++ b/caching/restore_emitter.cc
@@ -11,9 +11,10 @@ using namespace superblock_damage;
 namespace {
 	class restorer : public emitter {
 	public:
-		restorer(metadata::ptr md)
+		restorer(metadata::ptr md, bool clean_shutdown)
 			: in_superblock_(false),
-			  md_(md) {
+			  md_(md),
+			  clean_shutdown_(clean_shutdown) {
 		}
 
 		virtual ~restorer() {
@@ -44,7 +45,7 @@ namespace {
 		}
 
 		virtual void end_superblock() {
-			md_->commit();
+			md_->commit(clean_shutdown_);
 		}
 
 		virtual void begin_mappings() {
@@ -99,15 +100,16 @@ namespace {
 	private:
 		bool in_superblock_;
 		metadata::ptr md_;
+		bool clean_shutdown_;
 	};
 }
 
 //----------------------------------------------------------------
 
 emitter::ptr
-caching::create_restore_emitter(metadata::ptr md)
+caching::create_restore_emitter(metadata::ptr md, bool clean_shutdown)
 {
-	return emitter::ptr(new restorer(md));
+	return emitter::ptr(new restorer(md, clean_shutdown));
 }
 
 //----------------------------------------------------------------
diff --git a/caching/restore_emitter.h b/caching/restore_emitter.h
index 658dc68..9282895 100644
--- a/caching/restore_emitter.h
+++ b/caching/restore_emitter.h
@@ -7,7 +7,7 @@
 //----------------------------------------------------------------
 
 namespace caching {
-	emitter::ptr create_restore_emitter(metadata::ptr md);
+	emitter::ptr create_restore_emitter(metadata::ptr md, bool clean_shutdown = true);
 }
 
 //----------------------------------------------------------------
diff --git a/features/cache_restore.feature b/features/cache_restore.feature
index b9eef7d..1052089 100644
--- a/features/cache_restore.feature
+++ b/features/cache_restore.feature
@@ -21,6 +21,7 @@ Feature: thin_restore
       {-V|--version}
 
       {--debug-override-metadata-version} <integer>
+      {--omit-clean-shutdown}
 
     """
 
@@ -38,6 +39,7 @@ Feature: thin_restore
       {-V|--version}
 
       {--debug-override-metadata-version} <integer>
+      {--omit-clean-shutdown}
 
     """
 
@@ -72,3 +74,9 @@ Feature: thin_restore
     And an empty dev file
     When I run cache_restore with -i metadata.xml -o metadata.bin --debug-override-metadata-version 10298
     Then it should pass
+
+  Scenario: accepts --omit-clean-shutdown
+    Given a small xml file
+    And an empty dev file
+    When I run cache_restore with -i metadata.xml -o metadata.bin --omit-clean-shutdown
+    Then it should pass
diff --git a/persistent-data/data-structures/bitset.cc b/persistent-data/data-structures/bitset.cc
index c9ad0b4..1de628f 100644
--- a/persistent-data/data-structures/bitset.cc
+++ b/persistent-data/data-structures/bitset.cc
@@ -202,18 +202,18 @@ namespace persistent_data {
 
 //----------------------------------------------------------------
 
-bitset::bitset(tm_ptr tm)
+persistent_data::bitset::bitset(tm_ptr tm)
 	: impl_(new bitset_impl(tm))
 {
 }
 
-bitset::bitset(tm_ptr tm, block_address root, unsigned nr_bits)
+persistent_data::bitset::bitset(tm_ptr tm, block_address root, unsigned nr_bits)
 	: impl_(new bitset_impl(tm, root, nr_bits))
 {
 }
 
 block_address
-bitset::get_root() const
+persistent_data::bitset::get_root() const
 {
 	return impl_->get_root();
 }
@@ -225,37 +225,37 @@ bitset::get_nr_bits() const
 }
 
 void
-bitset::grow(unsigned new_nr_bits, bool default_value)
+persistent_data::bitset::grow(unsigned new_nr_bits, bool default_value)
 {
 	impl_->grow(new_nr_bits, default_value);
 }
 
 void
-bitset::destroy()
+persistent_data::bitset::destroy()
 {
 	impl_->destroy();
 }
 
 bool
-bitset::get(unsigned n)
+persistent_data::bitset::get(unsigned n)
 {
 	return impl_->get(n);
 }
 
 void
-bitset::set(unsigned n, bool value)
+persistent_data::bitset::set(unsigned n, bool value)
 {
 	impl_->set(n, value);
 }
 
 void
-bitset::flush()
+persistent_data::bitset::flush()
 {
 	impl_->flush();
 }
 
 void
-bitset::walk_bitset(bitset_visitor &v) const
+persistent_data::bitset::walk_bitset(bitset_visitor &v) const
 {
 	impl_->walk_bitset(v);
 }