diff --git a/httpx/_multipart.py b/httpx/_multipart.py
index 8bd7a17c9b..087448f9d6 100644
--- a/httpx/_multipart.py
+++ b/httpx/_multipart.py
@@ -205,7 +205,7 @@ def _iter_fields(
         self, data: dict, files: RequestFiles
     ) -> typing.Iterator[typing.Union[FileField, DataField]]:
         for name, value in data.items():
-            if isinstance(value, list):
+            if isinstance(value, (tuple, list)):
                 for item in value:
                     yield DataField(name=name, value=item)
             else: