diff --git a/hasql.cabal b/hasql.cabal
--- a/hasql.cabal
+++ b/hasql.cabal
@@ -1,7 +1,7 @@
 name:
   hasql
 version:
-  1
+  1.1
 category:
   Hasql, Database, PostgreSQL
 synopsis:
diff --git a/library/Hasql/Encoders.hs b/library/Hasql/Encoders.hs
--- a/library/Hasql/Encoders.hs
+++ b/library/Hasql/Encoders.hs
@@ -359,14 +359,10 @@
 -- Identifies the value with the PostgreSQL's \"unknown\" type,
 -- thus leaving it up to Postgres to infer the actual type of the value.
 -- 
--- The bytestring needs to be encoded according to the Postgres\' binary format
--- of the type it expects.
--- 
--- Essentially this is a low-level hook for encoding of values with custom codecs.
--- The
--- <http://hackage.haskell.org/package/postgresql-binary "postgresql-binary">
--- library will provide you with the toolchain.
--- 
+-- The value transimitted is any value encoded in the Postgres' Text data format.
+-- For reference, see the
+-- <https://www.postgresql.org/docs/10/static/protocol-overview.html#protocol-format-codes Formats and Format Codes>
+-- section of the Postgres' documentation.
 {-# INLINABLE unknown #-}
 unknown :: Value ByteString
 unknown =
diff --git a/library/Hasql/Private/Encoders/Params.hs b/library/Hasql/Private/Encoders/Params.hs
--- a/library/Hasql/Private/Encoders/Params.hs
+++ b/library/Hasql/Private/Encoders/Params.hs
@@ -28,7 +28,7 @@
     step (oid, bytesGetter) ~(oidList, bytesAndFormatList) =
       (,)
         (oid : oidList)
-        (fmap (\bytes -> (bytes, A.Binary)) (bytesGetter integerDatetimes) : bytesAndFormatList)
+        (fmap (\bytes -> (bytes, format oid)) (bytesGetter integerDatetimes) : bytesAndFormatList)
 
 run'' :: Params a -> a -> Bool -> [Maybe (A.Oid, ByteString, A.Format)]
 run'' (Params (Op op)) params integerDatetimes =
@@ -39,7 +39,12 @@
       mapping a : b
       where
         mapping (oid, bytesGetter) =
-          (,,) <$> pure oid <*> bytesGetter integerDatetimes <*> pure A.Binary
+          (,,) <$> pure oid <*> bytesGetter integerDatetimes <*> pure (format oid)
+
+format :: A.Oid -> A.Format
+format oid = case oid of
+  A.Oid 705 -> A.Text -- is unknown
+  _         -> A.Binary
 
 value :: C.Value a -> Params a
 value =
diff --git a/tasty/Main.hs b/tasty/Main.hs
--- a/tasty/Main.hs
+++ b/tasty/Main.hs
@@ -305,6 +305,37 @@
             in DSL.query "ok" query
       in actualIO >>= assertEqual "" (Right True)
     ,
+    testCase "Textual Unknown" $
+    let
+      actualIO =
+        DSL.session $ do
+          let
+            query =
+              Query.statement sql mempty Decoders.unit True
+              where
+                sql =
+                  "create or replace function overloaded(a int, b int) returns int as $$ select a + b $$ language sql;"
+            in DSL.query () query
+          let
+            query =
+              Query.statement sql mempty Decoders.unit True
+              where
+                sql =
+                  "create or replace function overloaded(a text, b text, c text) returns text as $$ select a || b || c $$ language sql;"
+            in DSL.query () query
+          let
+            query =
+              Query.statement sql encoder decoder True
+              where
+                sql =
+                  "select overloaded($1, $2) || overloaded($3, $4, $5)"
+                decoder =
+                  (Decoders.singleRow (Decoders.value (Decoders.text)))
+                encoder =
+                  contramany (Encoders.value Encoders.unknown)
+            in DSL.query ["1", "2", "4", "5", "6"] query
+      in actualIO >>= assertEqual "" (Right "3456")
+    ,
     testCase "Enum" $
     let
       actualIO =