diff --git a/src/stratocaster/base/strategy.py b/src/stratocaster/base/strategy.py
index a7e3d3e..327e4ce 100644
--- a/src/stratocaster/base/strategy.py
+++ b/src/stratocaster/base/strategy.py
@@ -33,7 +33,7 @@ def weights(self) -> dict[GufeKey, float | None]:
 
     def resolve(self) -> dict[GufeKey, float | None]:
         """Normalize the proposal weights relative to all non-None Transformation weights."""
-        weights = self.weights
+        weights = dict(self.weights)
         weight_sum = sum([weight for weight in weights.values() if weight is not None])
         modified_weights = {
             key: weight / weight_sum
diff --git a/src/stratocaster/tests/test_strategy_base.py b/src/stratocaster/tests/test_strategy_base.py
index 6b20058..fc890b4 100644
--- a/src/stratocaster/tests/test_strategy_base.py
+++ b/src/stratocaster/tests/test_strategy_base.py
@@ -17,6 +17,16 @@ class TestStrategyResult:
     def test_dict_roundtrip(self):
         assert StrategyResult.from_dict(self.result.to_dict()) == self.result
 
+    def test_resolve_does_not_mutate_weights(self):
+        original_weights = dict(self.result.weights)
+        self.result.resolve()
+        assert self.result.weights == original_weights
+
+    def test_resolve_is_idempotent(self):
+        first = self.result.resolve()
+        second = self.result.resolve()
+        assert first == second
+
 
 class DummyStrategySettings(StrategySettings):
     pass