diff --git a/src/handlers/main.lisp b/src/handlers/main.lisp
index b9edca6..5dcba04 100644
--- a/src/handlers/main.lisp
+++ b/src/handlers/main.lisp
@@ -10,6 +10,13 @@
   (remove-if #'string-empty-p
              (uiop:split-string uri :separator "/")))
 
+(defun get-resource-id (resource request)
+  (case resource
+    (survey (second (split-uri request)))))
+
+(defun get-survey-id (request)
+  (get-resource-id 'survey request))
+
 (defun today ()
   "Return today's date formatted as ISO-8601."
   (local-time:format-timestring nil
diff --git a/src/handlers/questionnaire.lisp b/src/handlers/questionnaire.lisp
index 7c646e2..77dbbec 100644
--- a/src/handlers/questionnaire.lisp
+++ b/src/handlers/questionnaire.lisp
@@ -19,6 +19,8 @@
         (t (error "Unsupported language: ~A" lang))))
 
 (defun process-questionnaire-get (lang s)
+  (check-type lang string)
+  (check-type s survey)
   (setf *html-lang* lang)
   (funcall (choose-sus-form lang) (survey-id s)))
 
@@ -31,7 +33,7 @@
     (ml-survey/views:questionnaire-submit)))
 
 (define-easy-handler (questionnaire :uri #'questionnaire-uri) (lang)
-  (let ((s (make-instance 'survey :id (second (split-uri (request-uri*))))))
+  (let ((s (make-instance 'survey :id (get-survey-id (request-uri*)))))
     (cond ((eq (hunchentoot:request-method*) :get)
            (process-questionnaire-get lang s))
           ((eq (hunchentoot:request-method*) :post)
diff --git a/src/handlers/survey.lisp b/src/handlers/survey.lisp
index 2d5a05c..665b3d0 100644
--- a/src/handlers/survey.lisp
+++ b/src/handlers/survey.lisp
@@ -90,7 +90,7 @@ Returns a list of integers."
   (survey-uri-p (request-uri request)))
 
 (define-easy-handler (survey :uri #'survey-uri) ()
-  (let ((s (make-instance 'survey :id (second (split-uri (request-uri*))))))
+  (let ((s (make-instance 'survey :id (get-survey-id (request-uri*)))))
     (ml-survey/views:survey s
                             (when (survey-data-dir-p s)
                               (sus-calc (survey-data-dir-files s))))))