diff --git a/powersimdata/utility/helpers.py b/powersimdata/utility/helpers.py
index 9aaec9228..a56534cb9 100644
--- a/powersimdata/utility/helpers.py
+++ b/powersimdata/utility/helpers.py
@@ -63,7 +63,7 @@ def put(self, key, obj):
         :param tuple key: a tuple used to lookup the cached value
         :param Any obj: the object to cache
         """
-        self._cache[key] = obj
+        self._cache[key] = copy.deepcopy(obj)
 
     def get(self, key):
         """Retrieve the value associated with key if it exists.
diff --git a/powersimdata/utility/tests/test_helpers.py b/powersimdata/utility/tests/test_helpers.py
index 7b75438c1..d6cea1552 100644
--- a/powersimdata/utility/tests/test_helpers.py
+++ b/powersimdata/utility/tests/test_helpers.py
@@ -68,6 +68,17 @@ def test_mem_cache_get_returns_copy():
     assert id(cache.get(key)) != id(obj)
 
 
+def test_mem_cache_put_version_never_changes():
+    cache = MemoryCache()
+    key = cache_key("foo", 4)
+    obj = {"key1": "value1"}
+    cache.put(key, obj)
+    obj["key2"] = "value2"
+    assert "key1" in cache.get(key)
+    assert "key2" not in cache.get(key)
+    assert "key2" in obj
+
+
 def test_copy_command():
     expected = r"\cp -p source dest"
     command = CommandBuilder.copy("source", "dest")