diff --git a/src/frozendict/cool.py b/src/frozendict/cool.py
index b38d027..46b0990 100644
--- a/src/frozendict/cool.py
+++ b/src/frozendict/cool.py
@@ -280,8 +280,8 @@ def deepfreeze(
     
     o_copy = copy(o)
     
-    for k, v in getItems(o)(o_copy):
-        o[k] = deepfreeze(
+    for k, v in getItems(o_copy)(o_copy):
+        o_copy[k] = deepfreeze(
             v,
             custom_converters = custom_converters,
             custom_inverse_converters = custom_inverse_converters
@@ -295,7 +295,7 @@ def deepfreeze(
         else:
             raise
     
-    return freeze(o)
+    return freeze(o_copy)
 
 
 __all__ = (
diff --git a/test/test_freeze.py b/test/test_freeze.py
index fcd85a3..4d00a60 100644
--- a/test/test_freeze.py
+++ b/test/test_freeze.py
@@ -181,4 +181,14 @@ def test_prefer_forward():
             custom_inverse_converters={FrozenSeqA: MutableSeq}
             )[0],
         FrozenSeqB
-        )
\ No newline at end of file
+        )
+
+def test_original_immutate():
+    unfrozen = {
+        "int": 1,
+        "nested": {"int": 1},
+    }
+
+    frozen = cool.deepfreeze(unfrozen)
+    
+    assert type(unfrozen["nested"]) is dict