diff --git a/scrapling/spiders/request.py b/scrapling/spiders/request.py
index faca233..ef766b2 100644
--- a/scrapling/spiders/request.py
+++ b/scrapling/spiders/request.py
@@ -22,6 +22,13 @@ def _convert_to_bytes(value: str | bytes) -> bytes:
     return value.encode(encoding="utf-8", errors="ignore")
 
 
+def _stable_value_repr(value: Any) -> str:
+    try:
+        return orjson.dumps(value, option=orjson.OPT_SORT_KEYS, default=repr).decode()
+    except TypeError:
+        return repr(value)
+
+
 class Request:
     def __init__(
         self,
@@ -98,7 +105,7 @@ class Request:
 
         if include_kwargs:
             filtered_kwargs = {
-                key.lower(): str(value)
+                key.lower(): _stable_value_repr(value)
                 for key, value in self._session_kwargs.items()
                 if key.lower() not in ("data", "json")
             }
diff --git a/tests/spiders/test_request.py b/tests/spiders/test_request.py
index f54f2cd..00f6c49 100644
--- a/tests/spiders/test_request.py
+++ b/tests/spiders/test_request.py
@@ -106,6 +106,24 @@ class TestRequestProperties:
 
         assert r1.update_fingerprint(include_kwargs=True) != r2.update_fingerprint(include_kwargs=True)
 
+    def test_fingerprint_include_kwargs_handles_non_primitive_values(self):
+        class _Opaque:
+            def __repr__(self) -> str:
+                return "_Opaque(stable)"
+
+        opaque = _Opaque()
+        r1 = Request("https://example.com", proxies={"http": "p1"}, custom=opaque)
+        r2 = Request("https://example.com", proxies={"http": "p1"}, custom=opaque)
+        r3 = Request("https://example.com", proxies={"http": "p2"}, custom=opaque)
+
+        fp1 = r1.update_fingerprint(include_kwargs=True)
+        r2._fp = None
+        fp2 = r2.update_fingerprint(include_kwargs=True)
+        fp3 = r3.update_fingerprint(include_kwargs=True)
+
+        assert fp1 == fp2
+        assert fp1 != fp3
+
     def test_fingerprint_include_headers_preserves_header_value_case(self):
         """Test header values are fingerprinted without lowercasing."""
         r1 = Request("https://example.com", headers={"X-Test": "A"})