diff --git a/CryDevice.cpp b/CryDevice.cpp
index 7bcc5912..37ada8d0 100644
--- a/CryDevice.cpp
+++ b/CryDevice.cpp
@@ -25,8 +25,10 @@ using blobstore::onblocks::BlobOnBlocks;
 
 namespace cryfs {
 
+constexpr uint32_t CryDevice::BLOCKSIZE_BYTES;
+
 CryDevice::CryDevice(unique_ptr<CryConfig> config, unique_ptr<BlockStore> blockStore)
-: _blobStore(make_unique<BlobStoreOnBlocks>(std::move(blockStore))), _rootKey(GetOrCreateRootKey(config.get())) {
+: _blobStore(make_unique<BlobStoreOnBlocks>(std::move(blockStore), BLOCKSIZE_BYTES)), _rootKey(GetOrCreateRootKey(config.get())) {
 }
 
 Key CryDevice::GetOrCreateRootKey(CryConfig *config) {
diff --git a/CryDevice.h b/CryDevice.h
index abf88d65..715d1c60 100644
--- a/CryDevice.h
+++ b/CryDevice.h
@@ -17,6 +17,8 @@ namespace bf = boost::filesystem;
 
 class CryDevice: public fspp::Device {
 public:
+  static constexpr uint32_t BLOCKSIZE_BYTES = 4096;
+
   CryDevice(std::unique_ptr<CryConfig> config, std::unique_ptr<blockstore::BlockStore> blockStore);
   virtual ~CryDevice();