diff --git a/src/api2/backup/environment.rs b/src/api2/backup/environment.rs
index 14859340..3a0a4c53 100644
--- a/src/api2/backup/environment.rs
+++ b/src/api2/backup/environment.rs
@@ -44,6 +44,7 @@ struct FixedWriterState {
     size: usize,
     chunk_size: u32,
     chunk_count: u64,
+    small_chunk_count: usize, // allow 0..1 small chunks (last chunk may be smaller)
     upload_stat: UploadStatistic,
 }
 
@@ -156,8 +157,13 @@ impl BackupEnvironment {
             None => bail!("fixed writer '{}' not registered", wid),
         };
 
-        if size != data.chunk_size {
-            bail!("fixed writer '{}' - got unexpected chunk size ({} != {}", data.name, size, data.chunk_size);
+        if size > data.chunk_size {
+            bail!("fixed writer '{}' - got large chunk ({} > {}", data.name, size, data.chunk_size);
+        } else if size < data.chunk_size {
+            data.small_chunk_count += 1;
+            if data.small_chunk_count > 1 {
+                bail!("fixed writer '{}' - detected multiple end chunks (chunk size too small)");
+            }
         }
 
         // record statistics
@@ -238,7 +244,7 @@ impl BackupEnvironment {
         let uid = state.next_uid();
 
         state.fixed_writers.insert(uid, FixedWriterState {
-            index, name, chunk_count: 0, size, chunk_size, upload_stat: UploadStatistic::new(),
+            index, name, chunk_count: 0, size, chunk_size, small_chunk_count: 0, upload_stat: UploadStatistic::new(),
         });
 
         Ok(uid)
@@ -280,14 +286,12 @@ impl BackupEnvironment {
             None => bail!("fixed writer '{}' not registered", wid),
         };
 
+        let end = (offset as usize) + (size as usize);
+        let idx = data.index.check_chunk_alignment(end, size as usize)?;
+
         data.chunk_count += 1;
 
-        if size != data.chunk_size {
-            bail!("fixed writer '{}' - got unexpected chunk size ({} != {}", data.name, size, data.chunk_size);
-        }
-
-        let pos = (offset as usize)/(data.chunk_size as usize);
-        data.index.add_digest(pos, digest)?;
+        data.index.add_digest(idx, digest)?;
 
         Ok(())
     }
diff --git a/src/backup/fixed_index.rs b/src/backup/fixed_index.rs
index 977d55f4..5d1937f3 100644
--- a/src/backup/fixed_index.rs
+++ b/src/backup/fixed_index.rs
@@ -298,33 +298,38 @@ impl FixedIndexWriter {
         Ok(index_csum)
     }
 
+    pub fn check_chunk_alignment(&self, offset: usize, chunk_len: usize) -> Result<usize, Error> {
+
+        if offset < chunk_len {
+            bail!("got chunk with small offset ({} < {}", offset, chunk_len);
+        }
+
+        let pos = offset - chunk_len;
+
+        if offset > self.size {
+            bail!("chunk data exceeds size ({} >= {})", offset, self.size);
+        }
+
+        // last chunk can be smaller
+        if ((offset != self.size) && (chunk_len != self.chunk_size)) ||
+            (chunk_len > self.chunk_size) || (chunk_len == 0) {
+                bail!("chunk with unexpected length ({} != {}", chunk_len, self.chunk_size);
+            }
+
+        if pos & (self.chunk_size-1) != 0 {
+            bail!("got unaligned chunk (pos = {})", pos);
+        }
+
+        Ok(pos / self.chunk_size)
+    }
+
     // Note: We want to add data out of order, so do not assume any order here.
     pub fn add_chunk(&mut self, chunk_info: &ChunkInfo, stat: &mut ChunkStat) -> Result<(), Error> {
 
         let chunk_len = chunk_info.chunk_len as usize;
-        let end = chunk_info.offset as usize;
+        let offset = chunk_info.offset as usize; // end of chunk
 
-        if end < chunk_len {
-            bail!("got chunk with small offset ({} < {}", end, chunk_len);
-        }
-
-        let pos = end - chunk_len;
-
-        if end > self.size {
-            bail!("write chunk data exceeds size ({} >= {})", end, self.size);
-        }
-
-        // last chunk can be smaller
-        if ((end != self.size) && (chunk_len != self.chunk_size)) ||
-            (chunk_len > self.chunk_size) || (chunk_len == 0) {
-                bail!("got chunk with wrong length ({} != {}", chunk_len, self.chunk_size);
-            }
-
-        if pos & (self.chunk_size-1) != 0 { bail!("add unaligned chunk (pos = {})", pos); }
-
-        if (end as u64) != chunk_info.offset {
-            bail!("got chunk with wrong offset ({} != {}", end, chunk_info.offset);
-        }
+        let idx = self.check_chunk_alignment(offset, chunk_len)?;
 
         let (is_duplicate, compressed_size) = self.store.insert_chunk(&chunk_info.chunk)?;
 
@@ -333,7 +338,7 @@ impl FixedIndexWriter {
 
         let digest = chunk_info.chunk.digest();
 
-        println!("ADD CHUNK {} {} {}% {} {}", pos, chunk_len,
+        println!("ADD CHUNK {} {} {}% {} {}", idx, chunk_len,
                  (compressed_size*100)/(chunk_len as u64), is_duplicate, proxmox::tools::digest_to_hex(digest));
 
         if is_duplicate {
@@ -342,7 +347,7 @@ impl FixedIndexWriter {
             stat.disk_size += compressed_size;
         }
 
-        self.add_digest(pos / self.chunk_size, digest)
+        self.add_digest(idx, digest)
     }
 
     pub fn add_digest(&mut self, index: usize, digest: &[u8; 32]) -> Result<(), Error> {