@@ -27,9 +27,11 @@
 from gitlab.const import *  # noqa
 from gitlab.exceptions import *  # noqa
 from gitlab import utils  # noqa
+from requests_toolbelt.multipart.encoder import MultipartEncoder
+
 
 __title__ = "python-gitlab"
-__version__ = "2.5.0"
+__version__ = "2.6.0"
 __author__ = "Gauvain Pocentek"
 __email__ = "gauvainpocentek@gmail.com"
 __license__ = "LGPL3"
@@ -496,9 +498,11 @@ def http_request(
 
         # We need to deal with json vs. data when uploading files
         if files:
-            data = post_data
             json = None
-            del opts["headers"]["Content-type"]
+            post_data["file"] = files.get("file")
+            post_data["avatar"] = files.get("avatar")
+            data = MultipartEncoder(post_data)
+            opts["headers"]["Content-type"] = data.content_type
         else:
             json = post_data
             data = None
@@ -509,9 +513,7 @@ def http_request(
         # The Requests behavior is right but it seems that web servers don't
         # always agree with this decision (this is the case with a default
         # gitlab installation)
-        req = requests.Request(
-            verb, url, json=json, data=data, params=params, files=files, **opts
-        )
+        req = requests.Request(verb, url, json=json, data=data, params=params, **opts)
         prepped = self.session.prepare_request(req)
         prepped.url = utils.sanitized_url(prepped.url)
         settings = self.session.merge_environment_settings(
 
@@ -1615,7 +1615,7 @@ def import_group(self, file, path, name, parent_id=None, **kwargs):
         Returns:
             dict: A representation of the import status.
         """
-        files = {"file": ("file.tar.gz", file)}
+        files = {"file": ("file.tar.gz", file, "application/octet-stream")}
         data = {"path": path, "name": name}
         if parent_id is not None:
             data["parent_id"] = parent_id
@@ -5488,8 +5488,8 @@ def import_project(
         Returns:
             dict: A representation of the import status.
         """
-        files = {"file": ("file.tar.gz", file)}
-        data = {"path": path, "overwrite": overwrite}
+        files = {"file": ("file.tar.gz", file, "application/octet-stream")}
+        data = {"path": path, "overwrite": str(overwrite)}
         if override_params:
             for k, v in override_params.items():
                 data["override_params[%s]" % k] = v
 
@@ -1 +1,2 @@
 requests==2.24.0
+requests-toolbelt>=0.9.1
@@ -26,7 +26,7 @@ def get_version():
     license="LGPLv3",
     url="https://github.com/python-gitlab/python-gitlab",
     packages=find_packages(),
-    install_requires=["requests>=2.22.0"],
+    install_requires=["requests>=2.22.0", "requests-toolbelt>=0.9.1"],
     python_requires=">=3.6.0",
     entry_points={"console_scripts": ["gitlab = gitlab.cli:main"]},
     classifiers=[