diff --git a/src/PIL/ImageShow.py b/src/PIL/ImageShow.py
index b6aa02261..103b7e1c7 100644
--- a/src/PIL/ImageShow.py
+++ b/src/PIL/ImageShow.py
@@ -279,7 +279,7 @@ class CommandViewer(Viewer):
         if not isinstance(command, str):
             raise TypeError(f"'command' must be 'str' not '{type(command)}'")
         values = {"file": quote(file), **options}
-        return command.format(values)
+        return command.format(**values)
 
 
 if __name__ == "__main__":