diff --git a/src/model/block.rs b/src/model/block.rs
index dd869802..ec714fef 100644
--- a/src/model/block.rs
+++ b/src/model/block.rs
@@ -158,22 +158,30 @@ impl BlockManager {
 		if self.is_block_compressed(hash).await.is_ok() {
 			return Ok(Message::Ok);
 		}
-		let _lock = self.data_dir_lock.lock().await;
 
 		let mut path = self.block_dir(hash);
-		fs::create_dir_all(&path).await?;
 
-		path.push(hex::encode(hash));
-		let buffer = match data {
-			BlockData::Plain(b) => b,
+		let (buffer, checksum) = match data {
+			BlockData::Plain(b) => (b, None),
 			BlockData::Compressed(b) => {
-				path.set_extension("zst");
-				b
+				let checksum = blake2sum(&b);
+				(b, Some(checksum))
 			}
 		};
 
+		let _lock = self.data_dir_lock.lock().await;
+
+		fs::create_dir_all(&path).await?;
+		path.push(hex::encode(hash));
+		if checksum.is_some() {
+			path.set_extension("zst.b2");
+		}
+
 		let mut f = fs::File::create(path).await?;
 		f.write_all(&buffer).await?;
+		if let Some(checksum) = checksum {
+			f.write_all(checksum.as_slice()).await?;
+		}
 		drop(f);
 
 		Ok(Message::Ok)
@@ -190,7 +198,7 @@ impl BlockManager {
 				f.map(|f| (f, false)).map_err(Into::into)
 			}
 			Ok(true) => {
-				path.set_extension("zst");
+				path.set_extension("zst.b2");
 				let f = fs::File::open(&path).await;
 				f.map(|f| (f, true)).map_err(Into::into)
 			}
@@ -207,14 +215,19 @@ impl BlockManager {
 		f.read_to_end(&mut data).await?;
 		drop(f);
 
-		let sum = if compressed {
-			zstd_decode(&data[..])
-				.ok()
-				.map(|decompressed| blake2sum(&decompressed[..]))
+		let sum_ok = if compressed {
+			if data.len() >= 32 {
+				let data_len = data.len() - 32;
+				let checksum = data.split_off(data_len);
+				blake2sum(&data[..]).as_slice() == &checksum
+			} else {
+				// the file is too short to be valid
+				false
+			}
 		} else {
-			Some(blake2sum(&data[..]))
+			blake2sum(&data[..]) == *hash
 		};
-		if sum.is_none() || sum.unwrap() != *hash {
+		if !sum_ok {
 			let _lock = self.data_dir_lock.lock().await;
 			warn!(
 				"Block {:?} is corrupted. Renaming to .corrupted and resyncing.",
@@ -257,11 +270,12 @@ impl BlockManager {
 
 	async fn is_block_compressed(&self, hash: &Hash) -> Result<bool, Error> {
 		let mut path = self.block_path(hash);
+		path.set_extension("zst.b2");
 		if fs::metadata(&path).await.is_ok() {
-			return Ok(false);
+			return Ok(true);
 		}
-		path.set_extension("zst");
-		fs::metadata(&path).await.map(|_| true).map_err(Into::into)
+		path.set_extension("");
+		fs::metadata(&path).await.map(|_| false).map_err(Into::into)
 	}
 
 	fn block_dir(&self, hash: &Hash) -> PathBuf {