diff --git a/lib/galaxy/datatypes/sniff.py b/lib/galaxy/datatypes/sniff.py
index 353462bb510..a3ccb86266f 100644
--- a/lib/galaxy/datatypes/sniff.py
+++ b/lib/galaxy/datatypes/sniff.py
@@ -64,15 +64,20 @@ def stream_to_open_named_file(stream, fd, filename, source_encoding=None, source
         codecs.lookup(target_encoding)
     except Exception:
         target_encoding = util.DEFAULT_ENCODING  # utf-8
+    use_source_encoding = source_encoding is not None
     while True:
         chunk = stream.read(CHUNK_SIZE)
         if not chunk:
             break
-        if source_encoding is not None:
+        if use_source_encoding:
             # If a source encoding is given we use it to convert to the target encoding
-            if not isinstance(chunk, text_type):
-                chunk = chunk.decode(source_encoding, source_error)
-            os.write(fd, chunk.encode(target_encoding, target_error))
+            try:
+                if not isinstance(chunk, text_type):
+                    chunk = chunk.decode(source_encoding, source_error)
+                os.write(fd, chunk.encode(target_encoding, target_error))
+            except UnicodeDecodeError:
+                use_source_encoding = False
+                os.write(fd, chunk)
         else:
             # Compressed files must be encoded after they are uncompressed in the upload utility,
             # while binary files should not be encoded at all.