diff --git a/src/pymoca/backends/casadi/api.py b/src/pymoca/backends/casadi/api.py
index <HASH>..<HASH> 100644
--- a/src/pymoca/backends/casadi/api.py
+++ b/src/pymoca/backends/casadi/api.py
@@ -240,7 +240,7 @@ def save_model(model_folder: str, model_name: str, model: Model,
 
         db['alias_relation'] = model.alias_relation
 
-        pickle.dump(db, f)
+        pickle.dump(db, f, protocol=-1)
 
 def load_model(model_folder: str, model_name: str, compiler_options: Dict[str, str]) -> CachedModel:
     """
Optimize loading cache using highest protocol pickle

The current highest protocol 4 results in about ~<I>% smaller files for
large models. Using timeit, the parsing is about ~<I>% faster, when both
pickles are paged into memory. If the pickle is not yet loaded in
memory, the reduced filesize will increase the speedup to ~<I>%.