diff --git a/lib/galaxy/datatypes/data.py b/lib/galaxy/datatypes/data.py
index e013f61040e..014a03cb8d0 100644
--- a/lib/galaxy/datatypes/data.py
+++ b/lib/galaxy/datatypes/data.py
@@ -453,7 +453,7 @@ class Data(metaclass=DataMeta):
                 mime = mimetypes.guess_type(file_path)[0]
                 if not mime:
                     try:
-                        mime = trans.app.datatypes_registry.get_mimetype_by_extension(".".split(file_path)[-1])
+                        mime = trans.app.datatypes_registry.get_mimetype_by_extension(file_path.split(".")[-1])
                     except Exception:
                         mime = "text/plain"
                 self._clean_and_set_mime_type(trans, mime, headers)
diff --git a/lib/galaxy/datatypes/display_applications/parameters.py b/lib/galaxy/datatypes/display_applications/parameters.py
index c1a28fc8147..911ade6de92 100644
--- a/lib/galaxy/datatypes/display_applications/parameters.py
+++ b/lib/galaxy/datatypes/display_applications/parameters.py
@@ -214,7 +214,7 @@ class DisplayParameterValueWrapper:
         if self.parameter.guess_mime_type:
             mime, encoding = mimetypes.guess_type(self._url)
             if not mime:
-                mime = self.trans.app.datatypes_registry.get_mimetype_by_extension(".".split(self._url)[-1], None)
+                mime = self.trans.app.datatypes_registry.get_mimetype_by_extension(self._url.split(".")[-1], None)
             if mime:
                 return mime
         return "text/plain"
@@ -269,10 +269,10 @@ class DisplayDataValueWrapper(DisplayParameterValueWrapper):
             if not mime:
                 if action_param_extra:
                     mime = self.trans.app.datatypes_registry.get_mimetype_by_extension(
-                        ".".split(action_param_extra)[-1], None
+                        action_param_extra.split(".")[-1], None
                     )
                 if not mime:
-                    mime = self.trans.app.datatypes_registry.get_mimetype_by_extension(".".split(self._url)[-1], None)
+                    mime = self.trans.app.datatypes_registry.get_mimetype_by_extension(self._url.split(".")[-1], None)
             if mime:
                 return mime
         if hasattr(self.value, "get_mime"):