diff --git a/src/stratocaster/base/strategy.py b/src/stratocaster/base/strategy.py
index 83cb30e..5817fc3 100644
--- a/src/stratocaster/base/strategy.py
+++ b/src/stratocaster/base/strategy.py
@@ -29,19 +29,18 @@ def _from_dict(cls, dct: dict):
 
     @property
     def weights(self) -> dict[GufeKey, float | None]:
-        return self._weights
+        return self._weights.copy()
 
     def resolve(self) -> dict[GufeKey, float | None]:
-        """Normalize the proposal weights relative to all non-None Transformation weights."""
-        weights = self.weights
-        weight_sum = sum([weight for weight in weights.values() if weight is not None])
-        modified_weights = {
-            key: weight / weight_sum
-            for key, weight in weights.items()
-            if weight is not None
+        """Get normalized proposal weights relative to all non-None Transformation weights."""
+        weight_sum = sum(
+            [weight for weight in self._weights.values() if weight is not None]
+        )
+        normalized_weights = {
+            key: weight / weight_sum if weight is not None else None
+            for key, weight in self._weights.items()
         }
-        weights.update(modified_weights)
-        return weights
+        return normalized_weights
 
     def __or__(self, other):
         if self.weights.keys() & other.weights.keys():
diff --git a/src/stratocaster/tests/test_strategy_base.py b/src/stratocaster/tests/test_strategy_base.py
index 6b20058..aaabf58 100644
--- a/src/stratocaster/tests/test_strategy_base.py
+++ b/src/stratocaster/tests/test_strategy_base.py
@@ -17,6 +17,17 @@ class TestStrategyResult:
     def test_dict_roundtrip(self):
         assert StrategyResult.from_dict(self.result.to_dict()) == self.result
 
+    def test_resolve_no_weight_side_effect(self):
+        """Resolve returns a normalized copy of the result
+        weights and doesn't modify the original data."""
+        res = self.result.resolve()
+        assert res != self.result.weights
+
+    def test_resolve_normalization(self):
+        """Resolve produces normalized weights for all non-None values."""
+        res = self.result.resolve()
+        assert 1 == sum([value for _, value in res.items() if value is not None])
+
 
 class DummyStrategySettings(StrategySettings):
     pass