diff --git a/src/Certificate.hs b/src/Certificate.hs
--- a/src/Certificate.hs
+++ b/src/Certificate.hs
@@ -64,6 +64,7 @@
     putStrLn "known extensions decoded: "
     showKnownExtension (X509.extensionGet es :: Maybe X509.ExtBasicConstraints)
     showKnownExtension (X509.extensionGet es :: Maybe X509.ExtKeyUsage)
+    showKnownExtension (X509.extensionGet es :: Maybe X509.ExtExtendedKeyUsage)
     showKnownExtension (X509.extensionGet es :: Maybe X509.ExtSubjectKeyId)
     showKnownExtension (X509.extensionGet es :: Maybe X509.ExtSubjectAltName)
     showKnownExtension (X509.extensionGet es :: Maybe X509.ExtAuthorityKeyId)
@@ -184,6 +185,7 @@
     | ShowHash
     | Validate
     | ValidationHost String
+    | Help
     deriving (Show,Eq)
 
 readPEMFile file = do
@@ -195,6 +197,9 @@
     return $ either error (map (X509.decodeSignedObject . pemContent)) $ pemParseBS content
 
 doCertMain opts files = do
+    when (Help `elem` opts) $ do
+        putStrLn $ usageInfo "usage: x509-util cert [options] <certificates>" optionsCert
+        exitSuccess
     objs <- readSignedObject (head files)
     forM_ objs $ \o ->
         case o of
@@ -259,6 +264,7 @@
     [ Option []     ["hash"] (NoArg ShowHash) "output certificate hash"
     , Option ['v']  ["validate"] (NoArg Validate) "validate certificate"
     , Option []     ["validation-host"] (ReqArg ValidationHost "host") "validation host use for validation"
+    , Option ['h']  ["help"] (NoArg Help) "show help"
     ]
 
 certMain = getoptMain optionsCert $ \o n -> doCertMain o n
@@ -266,6 +272,7 @@
 keyMain = getoptMain [] $ \o n -> doKeyMain n
 asn1Main = getoptMain [] $ \o n -> doASN1Main n
 
+getoptMain :: [OptDescr a] -> ([a] -> [String] -> IO ()) -> [String] -> IO ()
 getoptMain opts f as =
     case getOpt Permute opts as of
         (o,n,[])  -> f o n
diff --git a/x509-util.cabal b/x509-util.cabal
--- a/x509-util.cabal
+++ b/x509-util.cabal
@@ -1,5 +1,5 @@
 Name:                x509-util
-Version:             1.4.1
+Version:             1.4.2
 Description:         utility to parse, show, validate, sign and produce X509 certificates and chain.
 License:             BSD3
 License-file:        LICENSE
@@ -21,10 +21,10 @@
                    , bytestring
                    , text >= 0.11
                    , crypto-pubkey-types
-                   , x509
+                   , x509 >= 1.4.7
                    , x509-store
                    , x509-system
-                   , x509-validation >= 1.4.3
+                   , x509-validation >= 1.4.7
                    , asn1-types >= 0.2
                    , asn1-encoding
                    , pem