diff --git a/src/cmsplugin_blurp/renderers/data_source.py b/src/cmsplugin_blurp/renderers/data_source.py
index c825c3b..454c4e2 100644
--- a/src/cmsplugin_blurp/renderers/data_source.py
+++ b/src/cmsplugin_blurp/renderers/data_source.py
@@ -175,7 +175,7 @@ class Data(object):
             self.final_url = self.url
             if self.source.get('auth_mech', '').startswith('hmac'):
                 # remove the hmac- prefix
-                hash_algo = self.auth_mech[:5]
+                hash_algo = self.auth_mech[5:]
                 self.final_url = signature.sign_url(
                         self.final_url,
                         self.signature_key,