diff --git a/src/base-apis.js b/src/base-apis.js
index 07694596b11..883962c5a5c 100644
--- a/src/base-apis.js
+++ b/src/base-apis.js
@@ -364,14 +364,12 @@ MatrixBaseApis.prototype.getSsoLoginUrl = function(redirectUrl, loginType, idpId
         loginType = "sso";
     }
 
-    let prefix = PREFIX_R0;
     let url = "/login/" + loginType + "/redirect";
     if (idpId) {
         url += "/" + idpId;
-        prefix = "/_matrix/client/unstable/org.matrix.msc2858";
     }
 
-    return this._http.getUrl(url, { redirectUrl }, prefix);
+    return this._http.getUrl(url, { redirectUrl }, PREFIX_R0);
 };
 
 /**