diff --git a/src/pyrecest/utils/association_features.py b/src/pyrecest/utils/association_features.py
index 526fc1465..4bd2247f9 100644
--- a/src/pyrecest/utils/association_features.py
+++ b/src/pyrecest/utils/association_features.py
@@ -201,18 +201,40 @@ def _predict_proba_probability(self, features: Any) -> Any:
         return probabilities.reshape(original_shape)
 
     def _predict_proba_positive_class_index(self) -> int:
-        classes = getattr(self.model, "classes_", None)
-        if classes is None:
-            return 1
-        classes = asarray(classes).reshape(-1)
-        if classes.shape != (2,):
+        classes = _class_labels_to_list(getattr(self.model, "classes_", None))
+        if len(classes) != 2:
             return 1
         for class_index, class_label in enumerate(classes):
-            if bool(class_label == 1):
-                return class_index
+            try:
+                if bool(class_label == 1):
+                    return class_index
+            except (TypeError, ValueError):
+                continue
         return 1
 
 
+def _class_labels_to_list(classes: Any) -> list[Any]:
+    if classes is None:
+        return []
+    if hasattr(classes, "detach"):
+        classes = classes.detach().cpu()
+    if hasattr(classes, "reshape"):
+        try:
+            classes = classes.reshape(-1)
+        except TypeError:
+            pass
+    if hasattr(classes, "tolist"):
+        labels = classes.tolist()
+    else:
+        try:
+            labels = list(classes)
+        except TypeError:
+            return []
+    if isinstance(labels, list):
+        return labels
+    return [labels]
+
+
 def _normalize_feature_names(feature_names: Sequence[str]) -> tuple[str, ...]:
     if isinstance(feature_names, str):
         raise ValueError("feature_names must be a sequence of names, not a string")
diff --git a/tests/test_association_models.py b/tests/test_association_models.py
index fcfaaf741..e07a7f188 100644
--- a/tests/test_association_models.py
+++ b/tests/test_association_models.py
@@ -285,6 +285,23 @@ def predict_proba(self, features):
 
         npt.assert_allclose(probabilities, array([0.8, 0.3]))
 
+    def test_calibrated_predict_proba_falls_back_for_nonnumeric_classes(self):
+        class TextClassPredictProbaModel:
+            classes_ = ["not_a_match", "match"]
+
+            def predict_proba(self, features):
+                del features
+                return array([[0.8, 0.2], [0.3, 0.7]])
+
+        calibrated_model = CalibratedPairwiseAssociationModel(
+            TextClassPredictProbaModel(), feature_names=("distance", "similarity")
+        )
+        features = array([[0.1, 0.9], [2.0, 0.1]])
+
+        probabilities = calibrated_model.predict_match_probability(features)
+
+        npt.assert_allclose(probabilities, array([0.2, 0.7]))
+
 
 if __name__ == "__main__":
     unittest.main()