diff --git a/Lib/gftools/subsetmerger.py b/Lib/gftools/subsetmerger.py
index 9f42d7e0..5697411c 100644
--- a/Lib/gftools/subsetmerger.py
+++ b/Lib/gftools/subsetmerger.py
@@ -106,6 +106,8 @@ def add_subsets(self):
         for master in ds.sources:
             newpath = os.path.join(outpath, os.path.basename(master.path))
             target_ufo = open_ufo(master.path)
+            if master.layerName is not None:
+                continue
 
             master.path = newpath