diff --git a/platformio/project/config.py b/platformio/project/config.py
index 1ee27058..aadfbbb6 100644
--- a/platformio/project/config.py
+++ b/platformio/project/config.py
@@ -13,7 +13,6 @@
 # limitations under the License.
 
 import glob
-import io
 import json
 import os
 import re
@@ -449,7 +448,7 @@ class ProjectConfig(ProjectConfigBase, ProjectConfigDirsMixin):
         path = path or self.path
         if path in self._instances:
             del self._instances[path]
-        with io.open(path or self.path, mode="w+", encoding="utf8") as fp:
+        with open(path or self.path, "w+") as fp:
             fp.write(CONFIG_HEADER.strip() + "\n\n")
             self._parser.write(fp)
             fp.seek(0)