diff --git a/src/api2/admin/datastore/backup/environment.rs b/src/api2/admin/datastore/backup/environment.rs
index b99d9b29..cffa555b 100644
--- a/src/api2/admin/datastore/backup/environment.rs
+++ b/src/api2/admin/datastore/backup/environment.rs
@@ -158,14 +158,15 @@ impl BackupEnvironment {
             None => bail!("dynamic writer '{}' not registered", wid),
         };
 
-        data.offset += size as u64;
-        data.chunk_count += 1;
 
         if data.offset != offset {
             bail!("dynamic writer '{}' append chunk failed - got strange chunk offset ({} != {})",
                   data.name, data.offset, offset);
         }
 
+        data.offset += size as u64;
+        data.chunk_count += 1;
+
         data.index.add_chunk(data.offset, digest)?;
 
         Ok(())
diff --git a/src/client/http_client.rs b/src/client/http_client.rs
index a51e16a4..68fd974a 100644
--- a/src/client/http_client.rs
+++ b/src/client/http_client.rs
@@ -445,8 +445,9 @@ impl BackupClient {
         let stream = stream.
             map(move |data| {
                 let digest = openssl::sha::sha256(&data);
+                let offset = stream_len;
                 stream_len += data.len() as u64;
-                ChunkInfo { data, digest, offset: stream_len }
+                ChunkInfo { data, digest, offset }
             });
 
         let h2 = self.h2.clone();