diff --git a/src/scgenerator/spectra.py b/src/scgenerator/spectra.py
index edc89ec..734cf5b 100644
--- a/src/scgenerator/spectra.py
+++ b/src/scgenerator/spectra.py
@@ -191,6 +191,7 @@ def propagation(
     file_or_params: os.PathLike | Parameters,
     params: Parameters | None = None,
     bundle_data: bool = False,
+    overwrite: bool = False,
 ) -> Propagation:
     file = None
     if isinstance(file_or_params, Parameters):
@@ -198,7 +199,7 @@ def propagation(
     else:
         file = Path(file_or_params)
 
-    if file is not None and file.exists():
+    if file is not None and file.exists() and params is None:
         io = ZipFileIOHandler(file)
         return _open_existing_propagation(io)
 
@@ -206,6 +207,11 @@ def propagation(
         raise ValueError("Parameters must be specified to create new simulation")
 
     if file is not None:
+        if file.exists() and params is not None:
+            if overwrite:
+                Path(file).unlink()
+            else:
+                raise FileExistsError(f"{file} already exists. use overwrite=True to overwrite")
         io = ZipFileIOHandler(file)
     else:
         io = MemoryIOHandler()
diff --git a/tests/test_io_handlers.py b/tests/test_io_handlers.py
index e1a0457..deec0d9 100644
--- a/tests/test_io_handlers.py
+++ b/tests/test_io_handlers.py
@@ -101,6 +101,21 @@ def test_clear(tmp_path: Path):
     assert not zpath.exists()
 
 
+def test_overwrite(tmp_path: Path):
+    params = Parameters(**PARAMS)
+    zpath = tmp_path / "file.zip"
+    _ = propagation(zpath, params)
+    orig_file = zpath.read_bytes()
+
+    with pytest.raises(FileExistsError):
+        _ = propagation(zpath, params)
+
+    _ = propagation(zpath, params, overwrite=True)
+
+    assert zpath.read_bytes() != orig_file
+    assert len(zpath.read_bytes()) == len(orig_file)
+
+
 def test_zip_bundle(tmp_path: Path):
     params = Parameters(**PARAMS)