diff --git a/lib/galaxy/tools/parameters/basic.py b/lib/galaxy/tools/parameters/basic.py
index b5a8c30a875..4dace7797d7 100644
--- a/lib/galaxy/tools/parameters/basic.py
+++ b/lib/galaxy/tools/parameters/basic.py
@@ -1890,11 +1890,10 @@ class BaseDataToolParameter(ToolParameter):
         """
         Build list of classes for supported data formats
         """
-        self.extensions = input_source.get("format", "data").split(",")
+        self.extensions = [extension.strip().lower() for extension in input_source.get("format", "data").split(",")]
         formats = []
         if self.datatypes_registry:  # This may be None when self.tool.app is a ValidationContext
-            normalized_extensions = [extension.strip().lower() for extension in self.extensions]
-            for extension in normalized_extensions:
+            for extension in self.extensions:
                 datatype = self.datatypes_registry.get_datatype_by_extension(extension)
                 if datatype is not None:
                     formats.append(datatype)