diff --git a/examples/file1.txt b/examples/file1.txt
new file mode 100644
index 0000000..e69de29
diff --git a/examples/file_upload.py b/examples/file_upload.py
new file mode 100644
index 0000000..0f3fb3e
--- /dev/null
+++ b/examples/file_upload.py
@@ -0,0 +1,20 @@
+import uplink
+
+
+class HttpBin(uplink.Consumer):
+    @uplink.multipart
+    @uplink.post("post")
+    def post(self, attachments: uplink.PartMap):
+        pass
+
+
+client = HttpBin(base_url="https://httpbin.org/")
+
+
+print(
+    client.post(
+        attachments={
+            "file1.txt": [open("file1.txt", "rb"), open("file1.txt", "rb")]
+        }
+    )
+)
diff --git a/uplink/arguments.py b/uplink/arguments.py
index b38e6b3..c86a26d 100644
--- a/uplink/arguments.py
+++ b/uplink/arguments.py
@@ -604,7 +604,9 @@ def converter_key(self):
 
     def _modify_request(self, request_builder, value):
         """Updates the request body with the form part."""
-        request_builder.info["files"][self.name] = value
+        if "files" not in request_builder.info:
+            request_builder.info["files"] = []
+        request_builder.info["files"].append((self.name, value))
 
 
 class PartMap(TypedArgument):
@@ -628,9 +630,12 @@ def converter_key(self):
         """Converts each part to the request body."""
         return keys.Map(keys.CONVERT_TO_REQUEST_BODY)
 
-    def _modify_request(self, request_builder, value):
+    def _modify_request(self, request_builder, filemap):
         """Updates request body to with the form parts."""
-        request_builder.info["files"].update(value)
+        if "files" not in request_builder.info:
+            request_builder.info["files"] = []
+        for key in filemap:
+            request_builder.info["files"].append((key, filemap[key]))
 
 
 class Body(TypedArgument):