diff --git a/src/calng/Gotthard2Assembler.py b/src/calng/Gotthard2Assembler.py
index 58c86607fcd29bd81fd1150e93b6e1de345b50a6..02cb59e520d0c7a6132e0f6939331c817fca73a8 100644
--- a/src/calng/Gotthard2Assembler.py
+++ b/src/calng/Gotthard2Assembler.py
@@ -82,9 +82,9 @@ class Gotthard2Assembler(TrainMatcher.TrainMatcher):
         # figure out assembly mode and set handler
         if self.get("assemblyMode") == "auto":
             _, _, source_output = self._primary_source.partition(":")
-            if source_output.lower().endswith("streak"):
+            if "streak" in source_output.lower():
                 self.set("assemblyMode", "interleave2d")
-            elif source_output.lower().endswith("sums"):
+            elif "sums" in source_output.lower():
                 self.set("assemblyMode", "sum")
             else:
                 self.set("assemblyMode", "interleave1d")