diff --git a/src/Simplex/Messaging/Transport/Client.hs b/src/Simplex/Messaging/Transport/Client.hs
index f7af991a4..1a7f81992 100644
--- a/src/Simplex/Messaging/Transport/Client.hs
+++ b/src/Simplex/Messaging/Transport/Client.hs
@@ -26,6 +26,7 @@ import Data.Aeson (FromJSON (..), ToJSON (..))
 import qualified Data.Attoparsec.ByteString.Char8 as A
 import Data.ByteString.Char8 (ByteString)
 import qualified Data.ByteString.Char8 as B
+import Data.Char (isAsciiLower, isDigit)
 import Data.Default (def)
 import Data.List.NonEmpty (NonEmpty (..))
 import qualified Data.List.NonEmpty as L
@@ -70,11 +71,14 @@ instance StrEncoding TransportHost where
   strP =
     A.choice
       [ THIPv4 <$> ((,,,) <$> ipNum <*> ipNum <*> ipNum <*> A.decimal),
-        THOnionHost <$> ((<>) <$> A.takeTill (== '.') <*> A.string ".onion"),
-        THDomainName . B.unpack <$> A.takeWhile1 (A.notInClass ":#,;/ ")
+        THOnionHost <$> ((<>) <$> A.takeWhile (\c -> isAsciiLower c || isDigit c) <*> A.string ".onion"),
+        THDomainName . B.unpack <$> (notOnion <$?> A.takeWhile1 (A.notInClass ":#,;/ \n\r\t"))
       ]
     where
-      ipNum = A.decimal <* A.char '.'
+      ipNum = validIP <$?> (A.decimal <* A.char '.')
+      validIP :: Int -> Either String Word8
+      validIP n = if 0 <= n && n <= 255 then Right $ fromIntegral n else Left "invalid IP address"
+      notOnion s = if ".onion" `B.isSuffixOf` s then Left "invalid onion host" else Right s
 
 instance ToJSON TransportHost where
   toEncoding = strToJEncoding
diff --git a/tests/CoreTests/EncodingTests.hs b/tests/CoreTests/EncodingTests.hs
index 52ed73807..a89499777 100644
--- a/tests/CoreTests/EncodingTests.hs
+++ b/tests/CoreTests/EncodingTests.hs
@@ -1,4 +1,7 @@
+{-# LANGUAGE AllowAmbiguousTypes #-}
 {-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE ScopedTypeVariables #-}
+{-# LANGUAGE TypeApplications #-}
 
 module CoreTests.EncodingTests where
 
@@ -10,7 +13,9 @@ import Data.Int (Int64)
 import Data.Time.Clock.System (SystemTime (..), getSystemTime, utcToSystemTime)
 import Data.Time.ISO8601 (parseISO8601)
 import Simplex.Messaging.Encoding
+import Simplex.Messaging.Encoding.String
 import Simplex.Messaging.Parsers (parseAll)
+import Simplex.Messaging.Transport.Client (TransportHost (..))
 import Test.Hspec
 import Test.Hspec.QuickCheck (modifyMaxSuccess)
 import Test.QuickCheck
@@ -39,8 +44,36 @@ encodingTests = modifyMaxSuccess (const 1000) $ do
       testSystemTime t'
     it "parse(encode(SystemTime) should equal the same Int64" . property $
       \i -> parseAll smpP (smpEncode i) == Right (i :: Int64)
+  describe "Encoding transport hosts" $ do
+    describe "domain name hosts" $ do
+      it "should encode / decode domain name" $ THDomainName "smp.simplex.im" #==# "smp.simplex.im"
+      it "should not allow whitespace or punctuation" $ do
+        shouldNotParse @TransportHost "smp,simplex.im" "endOfInput"
+        shouldNotParse @TransportHost "smp:simplex.im" "endOfInput"
+        shouldNotParse @TransportHost "smp#simplex.im" "endOfInput"
+        shouldNotParse @TransportHost "smp simplex.im" "endOfInput"
+        shouldNotParse @TransportHost "smp\nsimplex.im" "endOfInput"
+    describe "onion hosts" $ do
+      it "should encode / decode onion host" $ THOnionHost "beccx4yfxxbvyhqypaavemqurytl6hozr47wfc7uuecacjqdvwpw2xid.onion" #==# "beccx4yfxxbvyhqypaavemqurytl6hozr47wfc7uuecacjqdvwpw2xid.onion"
+      it "should only allow latin letters and digits" $ do
+        shouldNotParse @TransportHost "beccx4yfxxbvyhqypaavemqurytl 6hozr47wfc7uuecacjqdvwpw2xid.onion" "endOfInput"
+        shouldNotParse @TransportHost "beccx4yfxxbvyhqypaavemqurytl\n6hozr47wfc7uuecacjqdvwpw2xid.onion" "endOfInput"
+        shouldNotParse @TransportHost "bèccx4yfxxbvyhqypaavemqurytl6hozr47wfc7uuecacjqdvwpw2xid.onion" "Failed reading: empty"
+    describe "IP address hosts" $ do
+      it "should encode / decode IP address" $ THIPv4 (192, 168, 0, 1) #==# "192.168.0.1"
+      it "should be valid" $ do
+        THDomainName "192.168.1" #==# "192.168.1"
+        THDomainName "192.256.0.1" #==# "192.256.0.1"
+        THDomainName "192.168.0.-1" #==# "192.168.0.-1"
+        shouldNotParse @TransportHost "192.168.0.0.1" "endOfInput"
   where
     testSystemTime :: SystemTime -> Expectation
     testSystemTime t = do
       smpEncode t `shouldBe` smpEncode (systemSeconds t)
-      parseAll smpP (smpEncode t) `shouldBe` Right t {systemNanoseconds = 0}
+      smpDecode (smpEncode t) `shouldBe` Right t {systemNanoseconds = 0}
+    (#==#) :: (StrEncoding s, Eq s, Show s) => s -> ByteString -> Expectation
+    (#==#) x s = do
+      strEncode x `shouldBe` s
+      strDecode s `shouldBe` Right x
+    shouldNotParse :: forall s. (StrEncoding s, Eq s, Show s) => ByteString -> String -> Expectation
+    shouldNotParse s err = strDecode s `shouldBe` (Left err :: Either String s)