diff --git a/add_webmention.py b/add_webmention.py
index 1105640..0175327 100644
--- a/add_webmention.py
+++ b/add_webmention.py
@@ -21,7 +21,7 @@ CACHE_TIME = datetime.timedelta(seconds=15)
 def add_wm(url=None):
     """Proxies HTTP requests and adds Link header to our webmention endpoint."""
     url = urllib.parse.unquote(url)
-    if not url.startswith('http://') and not url.startswith('https://'):
+    if not util.is_web(url):
         error('URL must start with http:// or https://')
 
     try:
diff --git a/follow.py b/follow.py
index ce189f7..44b200f 100644
--- a/follow.py
+++ b/follow.py
@@ -36,7 +36,7 @@ def remote_follow():
     if len(split) == 2:
         addr_domain = split[1]
         resource = f'acct:{addr}'
-    elif addr.startswith('http://') or addr.startswith('https://'):
+    elif util.is_web(addr):
         addr_domain = util.domain_from_link(addr, minimize=False)
         resource = addr
     else:
diff --git a/redirect.py b/redirect.py
index c4dffe5..9c19ef7 100644
--- a/redirect.py
+++ b/redirect.py
@@ -43,7 +43,7 @@ def redir(to):
     # if that happened to this URL, expand it back to two /s.
     to = re.sub(r'^(https?:/)([^/])', r'\1/\2', to)
 
-    if not to.startswith('http://') and not to.startswith('https://'):
+    if not util.is_web(to):
         error(f'Expected fully qualified URL; got {to}')
 
     # check that we've seen this domain before so we're not an open redirect
diff --git a/webfinger.py b/webfinger.py
index 3564823..fb0b39a 100644
--- a/webfinger.py
+++ b/webfinger.py
@@ -186,7 +186,7 @@ class Webfinger(Actor):
             domain = urllib.parse.urlparse(resource).netloc or resource
 
         url = None
-        if resource.startswith('http://') or resource.startswith('https://'):
+        if util.is_web(resource):
             url = resource
 
         return super().template_vars(domain=domain, url=url)