diff --git a/preprocess.py b/preprocess.py
index b014e1cdab553b93e4555f3bbcc90f0ca4aab372..34f646029cbd9d223b1e0b5c0833a06c506cdb95 100644
--- a/preprocess.py
+++ b/preprocess.py
@@ -245,7 +245,7 @@ def S2_THEIA_preprocess(fld, cmask=False, ref=None, bandlist=None):
     '''
 
     # new stack generation
-    stack_fn = glob.glob(fld + '/*_FRE_B2*.tif')[0].replace('B2', 'STACK')
+    stack_fn = bnd_ref[0].replace(ref, 'STACK')
     cmd = ['otbcli_ConcatenateImages','-il'] + bnd_tomerge + ['-out', stack_fn, 'uint16']
     subprocess.call(cmd, shell=sh)
     setNoDataValue(stack_fn, 0)