diff --git a/src/ffx/ffx.py b/src/ffx/ffx.py
index 39a091f..94fd0ce 100755
--- a/src/ffx/ffx.py
+++ b/src/ffx/ffx.py
@@ -725,7 +725,7 @@ def convert(ctx,
             for filterYield in chainIteration:
                 targetFilenameTokens += filterYield['suffices']
 
-            targetFilename = f"{'_'.join(targetFilenameTokens)}.{targetExtension}"
+            targetFilename = f"{'_'.join(targetFilenameTokens)}.{sourceFilenameExtension if rename_only else targetExtension}"
 
             targetPath = os.path.join(output_directory, targetFilename) if output_directory else targetFilename