diff --git a/lib/mergeset/block_stream_reader.go b/lib/mergeset/block_stream_reader.go
index 984f3035b..64faa9f47 100644
--- a/lib/mergeset/block_stream_reader.go
+++ b/lib/mergeset/block_stream_reader.go
@@ -91,6 +91,13 @@ func (bsr *blockStreamReader) reset() {
 	bsr.err = nil
 }
 
+func (bsr *blockStreamReader) String() string {
+	if len(bsr.path) > 0 {
+		return bsr.path
+	}
+	return bsr.ph.String()
+}
+
 // InitFromInmemoryPart initializes bsr from the given ip.
 func (bsr *blockStreamReader) InitFromInmemoryPart(ip *inmemoryPart) {
 	bsr.reset()
diff --git a/lib/mergeset/merge.go b/lib/mergeset/merge.go
index 039ad34d7..2387c793a 100644
--- a/lib/mergeset/merge.go
+++ b/lib/mergeset/merge.go
@@ -29,7 +29,7 @@ func mergeBlockStreams(ph *partHeader, bsw *blockStreamWriter, bsrs []*blockStre
 	if err == errForciblyStopped {
 		return err
 	}
-	return fmt.Errorf("cannot merge block streams: %s", err)
+	return fmt.Errorf("cannot merge %d block streams: %s: %s", len(bsrs), bsrs, err)
 }
 
 var bsmPool = &sync.Pool{
diff --git a/lib/storage/merge.go b/lib/storage/merge.go
index 29da58c0e..524b8a4d1 100644
--- a/lib/storage/merge.go
+++ b/lib/storage/merge.go
@@ -29,7 +29,7 @@ func mergeBlockStreams(ph *partHeader, bsw *blockStreamWriter, bsrs []*blockStre
 	if err == errForciblyStopped {
 		return err
 	}
-	return fmt.Errorf("cannot merge %d streams: %s", len(bsrs), err)
+	return fmt.Errorf("cannot merge %d streams: %s: %s", len(bsrs), bsrs, err)
 }
 
 var bsmPool = &sync.Pool{