diff --git a/webarchiv.py b/webarchiv.py
index 0fb6bd17fe9a069904fb5985a6b5c341c3e09736..2138d85aef85c64e765fdc3a60999749aac199cf 100644
--- a/webarchiv.py
+++ b/webarchiv.py
@@ -36,7 +36,7 @@ class WebarchivSession:
         with a single positional format string placeholder
         for the REST operation and parameters.
         """
-        return 'https://webarchiv.onb.ac.at/api/'
+        return 'https://webarchiv.onb.ac.at/api'
 
     @property
     def base_url(self):
@@ -45,7 +45,7 @@ class WebarchivSession:
         with a single positional format string placeholder
         for the REST operation and parameters.
         """
-        return self.api_path + '/{}'
+        return self.api_path + '{}'
 
     @property
     def _error_template(self):
@@ -80,7 +80,7 @@ class WebarchivSession:
         else:
             fingerprint = ''
 
-        r = requests.post(self.base_url.format('authentication'),
+        r = requests.post(self.base_url.format('/authentication'),
                           data='''{{
                               "apikey": "{api_key}",
                               "fingerprint": "{fingerprint}",