diff --git a/persistent-data/block.tcc b/persistent-data/block.tcc
index be55c23..e9da86a 100644
--- a/persistent-data/block.tcc
+++ b/persistent-data/block.tcc
@@ -325,7 +325,7 @@ typename block_manager<BlockSize>::write_ref
 block_manager<BlockSize>::superblock(block_address location,
 				     typename block_manager<BlockSize>::validator::ptr v)
 {
-	tracker_.write_lock(location);
+	tracker_.superblock_lock(location);
 	try {
 		check(location);
 
@@ -353,7 +353,7 @@ typename block_manager<BlockSize>::write_ref
 block_manager<BlockSize>::superblock_zero(block_address location,
 					  typename block_manager<BlockSize>::validator::ptr v)
 {
-	tracker_.write_lock(location);
+	tracker_.superblock_lock(location);
 	try {
 		check(location);
 
diff --git a/persistent-data/lock_tracker.cc b/persistent-data/lock_tracker.cc
index b7c3f48..b21aa54 100644
--- a/persistent-data/lock_tracker.cc
+++ b/persistent-data/lock_tracker.cc
@@ -59,6 +59,21 @@ lock_tracker::write_lock(uint64_t key)
 	locks_.insert(make_pair(key, -1));
 }
 
+void
+lock_tracker::superblock_lock(uint64_t key)
+{
+	if (superblock_)
+		throw runtime_error("superblock already held");
+
+	superblock_ = boost::optional<uint64_t>(key);
+	try {
+		write_lock(key);
+
+	} catch (...) {
+		superblock_ = boost::optional<uint64_t>();
+	}
+}
+
 void
 lock_tracker::unlock(uint64_t key)
 {
@@ -72,6 +87,9 @@ lock_tracker::unlock(uint64_t key)
 		locks_.insert(make_pair(key, it->second - 1));
 	else
 		locks_.erase(key);
+
+	if (superblock_ && *superblock_ == key)
+		superblock_ = boost::optional<uint64_t>();
 }
 
 bool
diff --git a/persistent-data/lock_tracker.h b/persistent-data/lock_tracker.h
index 8541d83..f54ad42 100644
--- a/persistent-data/lock_tracker.h
+++ b/persistent-data/lock_tracker.h
@@ -20,6 +20,7 @@
 #define LOCK_TRACKER_H
 
 #include <boost/noncopyable.hpp>
+#include <boost/optional.hpp>
 #include <map>
 #include <stdint.h>
 
@@ -33,6 +34,7 @@ namespace persistent_data {
 
 		void read_lock(uint64_t key);
 		void write_lock(uint64_t key);
+		void superblock_lock(uint64_t key);
 		void unlock(uint64_t key);
 
 	private:
@@ -45,6 +47,7 @@ namespace persistent_data {
 
 		// Positive for read lock, negative for write lock
 		LockMap locks_;
+		boost::optional<uint64_t> superblock_;
 
 		uint64_t low_;
 		uint64_t high_;