diff --git a/src/niquests/models.py b/src/niquests/models.py
index 348affafae..f15106c4e2 100644
--- a/src/niquests/models.py
+++ b/src/niquests/models.py
@@ -742,9 +742,12 @@ def _encode_params(
             result = []
             for k, vs in to_key_val_list(data):
                 iterable_vs: typing.Iterable[str | bytes]
-                if isinstance(vs, (str, bytes, int, float, bool)):
-                    # not officially supported, but some people maybe passing ints, float or bool.
-                    if isinstance(vs, (str, bytes)) is False:
+                if isinstance(vs, (str, bytes, int, float, bool)) or not hasattr(
+                    vs, "__iter__"
+                ):
+                    # not officially supported, but some people maybe passing ints, float, bool,
+                    # or other string serializable classes.
+                    if not isinstance(vs, (str, bytes)):
                         iterable_vs = [str(vs)]
                     else:
                         iterable_vs = [vs]
diff --git a/tests/test_requests.py b/tests/test_requests.py
index ec58550fe2..a957a254c8 100644
--- a/tests/test_requests.py
+++ b/tests/test_requests.py
@@ -2540,6 +2540,28 @@ def test_json_encodes_as_bytes():
     assert isinstance(p.body, bytes)
 
 
+def test_data_ecodes_noniterables():
+    class Class:
+        pass
+
+    class ClassStringable:
+        def __str__(self):
+            return "🔥arbClassStringable🔥"
+
+    body = {
+        "string": "string",
+        "float": 0.01,
+        "int": 100,
+        "bool": True,
+        "None": None,
+        "plain_class": Class(),
+        "stringable_class": ClassStringable(),
+    }
+    p = PreparedRequest()
+    p.prepare(method="post", url="https://www.example.com/", data=body)
+    assert isinstance(p.body, str)
+
+
 def test_requests_are_updated_each_time(httpbin):
     session = RedirectSession([303, 307])
     prep = niquests.Request("POST", httpbin("post")).prepare()