diff --git a/src/signature_mahalanobis_knn/sig_mahal_knn.py b/src/signature_mahalanobis_knn/sig_mahal_knn.py
index 38c6dbc..5e4d97c 100644
--- a/src/signature_mahalanobis_knn/sig_mahal_knn.py
+++ b/src/signature_mahalanobis_knn/sig_mahal_knn.py
@@ -106,17 +106,25 @@ def fit(
             )
 
             # set default kwargs for signature transformer if not provided
-            if signature_kwargs is None or signature_kwargs == {}:
-                signature_kwargs = {
-                    "augmentation_list": ("addtime",),
-                    "window_name": "global",
-                    "window_depth": None,
-                    "window_length": None,
-                    "window_step": None,
-                    "rescaling": None,
-                    "sig_tfm": "signature",
-                    "depth": 2,
-                }
+            sig_defaults = {
+                "augmentation_list": ("addtime",),
+                "window_name": "global",
+                "window_depth": None,
+                "window_length": None,
+                "window_step": None,
+                "rescaling": None,
+                "sig_tfm": "signature",
+                "depth": 2,
+            }
+
+            if signature_kwargs is None:
+                # set all defaults
+                signature_kwargs = sig_defaults
+            else:
+                # set defaults for any missing kwargs
+                for key, value in sig_defaults.items():
+                    if key not in signature_kwargs:
+                        signature_kwargs[key] = value
 
             self.signature_transform = SignatureTransformer(
                 **signature_kwargs,