diff --git a/data-serializer.cabal b/data-serializer.cabal
--- a/data-serializer.cabal
+++ b/data-serializer.cabal
@@ -1,5 +1,5 @@
 Name: data-serializer
-Version: 0.3.3
+Version: 0.3.4
 Category: Data
 Stability: experimental
 Synopsis: Common API for serialization libraries
diff --git a/src/Data/Deserializer.hs b/src/Data/Deserializer.hs
--- a/src/Data/Deserializer.hs
+++ b/src/Data/Deserializer.hs
@@ -215,6 +215,10 @@
   ensure_ ∷ Int → μ ()
   ensure_ = (() <$) . ensure
   {-# INLINE ensure_ #-}
+  -- | 'check' /n/ returns 'True' if the input has at least /n/ more bytes.
+  check ∷ Int → μ Bool
+  check n = True <$ ensure_ n <|> return False
+  {-# INLINE check #-}
   -- | Consume exactly the given number of bytes.
   take ∷ Int → μ BS.ByteString
   -- | Consume a portion of the input (the size of the returned