diff --git a/wikitools3/api.py b/wikitools3/api.py
index 6ba2e5a..25d305e 100644
--- a/wikitools3/api.py
+++ b/wikitools3/api.py
@@ -96,7 +96,7 @@ def __init__(self, wiki, data, write=False, multipart=False):
         self.response = False
         if wiki.auth:
             self.headers["Authorization"] = "Basic {0}".format(
-                base64.encodestring(f"{wiki.auth}:{wiki.httppass}")
+                base64.encodestring(f"{wiki.auth}:{wiki.httppass}".encode()).decode()
             ).replace("\n", "")
         if hasattr(wiki, "passman"):
             self.opener = urllib.request.build_opener(