diff --git a/timefold-solver-python-core/src/main/java/ai/timefold/solver/python/score/constraint/ConstraintRefPythonJavaTypeMapping.java b/timefold-solver-python-core/src/main/java/ai/timefold/solver/python/score/constraint/ConstraintRefPythonJavaTypeMapping.java
index 1654414..15dc8de 100644
--- a/timefold-solver-python-core/src/main/java/ai/timefold/solver/python/score/constraint/ConstraintRefPythonJavaTypeMapping.java
+++ b/timefold-solver-python-core/src/main/java/ai/timefold/solver/python/score/constraint/ConstraintRefPythonJavaTypeMapping.java
@@ -50,8 +50,8 @@ public PythonLikeObject toPythonObject(ConstraintRef javaObject) {
     @Override
     public ConstraintRef toJavaObject(PythonLikeObject pythonObject) {
         try {
-            var packageName = ((PythonString) packageNameField.get(pythonObject)).value.toString();
-            var constraintName = ((PythonString) constraintNameField.get(pythonObject)).value.toString();
+            var packageName = ((PythonString) packageNameField.get(pythonObject)).value;
+            var constraintName = ((PythonString) constraintNameField.get(pythonObject)).value;
             return ConstraintRef.of(packageName, constraintName);
         } catch (IllegalAccessException e) {
             throw new RuntimeException(e);
diff --git a/timefold-solver-python-core/src/main/python/score/_score_analysis.py b/timefold-solver-python-core/src/main/python/score/_score_analysis.py
index 08ab098..2d8a9d8 100644
--- a/timefold-solver-python-core/src/main/python/score/_score_analysis.py
+++ b/timefold-solver-python-core/src/main/python/score/_score_analysis.py
@@ -57,7 +57,7 @@ def constraint_id(self) -> str:
     @staticmethod
     def parse_id(constraint_id: str):
         slash_index = constraint_id.rfind('/')
-        if slash_index == -1: raise RuntimeError(
+        if slash_index == -1: raise IndexError(
             f'The constraint_id {constraint_id} is invalid as it does not contain a package separator \'/\'.')
         package_name = constraint_id[:slash_index]
         constraint_name = constraint_id[slash_index + 1:]