diff --git a/src/github.com/matrix-org/dendrite/clientapi/routing/auth_fallback.go b/src/github.com/matrix-org/dendrite/clientapi/routing/auth_fallback.go
index 386b6ceab..f786e2b15 100644
--- a/src/github.com/matrix-org/dendrite/clientapi/routing/auth_fallback.go
+++ b/src/github.com/matrix-org/dendrite/clientapi/routing/auth_fallback.go
@@ -101,9 +101,10 @@ func ServeTemplate(w http.ResponseWriter, templateHTML string, data map[string]s
 
 // AuthFallback implements GET on /auth/{authType}/fallback/web?session={sessionID}
 func AuthFallback(
-	w http.ResponseWriter, req *http.Request, authType string, sessionID string,
+	w http.ResponseWriter, req *http.Request, authType string,
 	cfg config.Dendrite,
 ) *util.JSONResponse {
+	sessionID := req.Form.Get("session")
 	ServeRecaptcha := func() {
 		data := map[string]string{
 			"MyUrl":   req.URL.String(),
diff --git a/src/github.com/matrix-org/dendrite/clientapi/routing/routing.go b/src/github.com/matrix-org/dendrite/clientapi/routing/routing.go
index 0b4eb37ef..6c5f4bd2f 100644
--- a/src/github.com/matrix-org/dendrite/clientapi/routing/routing.go
+++ b/src/github.com/matrix-org/dendrite/clientapi/routing/routing.go
@@ -174,10 +174,10 @@ func Setup(
 		}),
 	).Methods("GET", "POST", "OPTIONS")
 
-	r0mux.Handle("/auth/{authType}/fallback/web?session={sessionID}",
+	r0mux.Handle("/auth/{authType}/fallback/web",
 		common.MakeHTMLAPI("authfallback", func(w http.ResponseWriter, req *http.Request) *util.JSONResponse {
 			vars := mux.Vars(req)
-			return AuthFallback(w, req, vars["authType"], vars["sessionID"], cfg)
+			return AuthFallback(w, req, vars["authType"], cfg)
 		}),
 	).Methods("GET", "POST", "OPTIONS")