diff --git a/src/Network/FedURI.hs b/src/Network/FedURI.hs
index 52a1644..031e651 100644
--- a/src/Network/FedURI.hs
+++ b/src/Network/FedURI.hs
@@ -38,6 +38,7 @@ import Prelude
 import Control.Monad ((<=<))
 import Data.Aeson
 import Data.Bifunctor (bimap, first)
+import Data.Char
 import Data.Hashable
 import Data.Maybe (fromJust)
 import Data.Text (Text)
@@ -53,6 +54,7 @@ import qualified Data.Text as T (pack, unpack, stripPrefix)
 -- * The scheme is HTTPS
 -- * The authority part is present
 -- * The authority part doesn't have userinfo
+-- * The authority host needs to match certain rules
 -- * The authority part doesn't have a port number
 -- * There is no query part
 -- * A fragment part may be present
@@ -96,6 +98,12 @@ parseFedURI t = do
     if p == ""
         then Right ()
         else Left "URI has non-empty port"
+    if any (== '.') h
+        then Right ()
+        else Left "Host doesn't contain periods"
+    if any isAsciiLetter h
+        then Right ()
+        else Left "Host doesn't contain ASCII letters"
     if uriQuery uri == ""
         then Right ()
         else Left "URI query is non-empty"
@@ -104,6 +112,8 @@ parseFedURI t = do
         , furiPath     = T.pack $ uriPath uri
         , furiFragment = T.pack $ uriFragment uri
         }
+    where
+    isAsciiLetter c = isAsciiLower c || isAsciiUpper c
 
 toURI :: FedURI -> URI
 toURI (FedURI h p f) = URI
diff --git a/src/Vervis/Foundation.hs b/src/Vervis/Foundation.hs
index 14b7879..0ed9d0d 100644
--- a/src/Vervis/Foundation.hs
+++ b/src/Vervis/Foundation.hs
@@ -777,10 +777,6 @@ instance YesodHttpSig App where
                 Left e -> throwE $ "keyId in Sig header isn't a valid FedURI: " ++ e
                 Right u -> return u
         checkHost h = do
-            unless (T.any (== '.') h) $
-                throwE "Host doesn't contain periods"
-            unless (T.any isAsciiLetter h) $
-                throwE "Host doesn't contain ASCII letters"
             home <- getsYesod $ appInstanceHost . appSettings
             when (h == home) $
                 throwE "Received HTTP signed request from the instance's host"