diff --git a/README.md b/README.md
--- a/README.md
+++ b/README.md
@@ -16,31 +16,39 @@
 
 ## Type Classes
 
-### `IsScalar`
+### `IsPrimitive`
 
 The core type class for types that map to PostgreSQL values:
 
 ```haskell
-class IsScalar a where
+class IsPrimitive a where
   -- Type metadata
   typeName :: Tagged a Text
   baseOid :: Tagged a (Maybe Word32)
   arrayOid :: Tagged a (Maybe Word32)
   typeParams :: Tagged a [Text]
   typeSignature :: Tagged a Text
-  
-  -- Binary format
-  binaryEncoder :: a -> Write.Write
-  binaryDecoder :: PtrPeeker.Variable (Either DecodingError a)
-  
+
   -- Textual format
   textualEncoder :: a -> TextBuilder.TextBuilder
   textualDecoder :: Attoparsec.Parser a
 ```
 
-This class enables:
-- **Binary encoding/decoding** using PostgreSQL's native binary format
-- **Textual encoding/decoding** using PostgreSQL's text representation  
+### `IsBinaryPrimitive`
+
+Evidence that a type additionally has a PostgreSQL binary wire format. Not every PostgreSQL type
+supports binary transmission — some only have textual `send`/`receive` functions registered on the
+server — so this is a separate, optional subclass rather than part of `IsPrimitive` itself:
+
+```haskell
+class (IsPrimitive a) => IsBinaryPrimitive a where
+  binaryEncoder :: a -> Write.Write
+  binaryDecoder :: PtrPeeker.Variable (Either DecodingError a)
+```
+
+These classes enable:
+- **Binary encoding/decoding** using PostgreSQL's native binary format, where supported
+- **Textual encoding/decoding** using PostgreSQL's text representation
 - **Type metadata** including OIDs and type signatures for parameterized types
 - **Round-trip fidelity** through all encoding combinations
 
@@ -51,7 +59,7 @@
 Use this package to:
 - Define custom PostgreSQL type mappings compatible with the "postgresql-types" ecosystem
 - Create adapter libraries for different PostgreSQL client libraries
-- Build generic tools that work with any `IsScalar` instance
+- Build generic tools that work with any `IsPrimitive` (and, where applicable, `IsBinaryPrimitive`) instance
 
 ### For Application Developers
 
diff --git a/postgresql-types-algebra.cabal b/postgresql-types-algebra.cabal
--- a/postgresql-types-algebra.cabal
+++ b/postgresql-types-algebra.cabal
@@ -1,6 +1,6 @@
 cabal-version: 3.0
 name: postgresql-types-algebra
-version: 0.1.0.1
+version: 0.2
 category: PostgreSQL, Codecs
 synopsis: Type classes for PostgreSQL type mappings
 description:
diff --git a/src/library/PostgresqlTypes/Algebra.hs b/src/library/PostgresqlTypes/Algebra.hs
--- a/src/library/PostgresqlTypes/Algebra.hs
+++ b/src/library/PostgresqlTypes/Algebra.hs
@@ -11,8 +11,8 @@
 import qualified TextBuilder
 import Prelude
 
--- | Evidence that a type maps to a PostgreSQL scalar value.
-class IsScalar a where
+-- | Evidence that a type maps to a PostgreSQL primitive type.
+class IsPrimitive a where
   -- | PostgreSQL schema name, if applicable.
   schemaName :: Tagged a (Maybe Text)
 
@@ -34,7 +34,12 @@
   -- | Get the PostgreSQL type signature for a given Haskell type.
   --
   -- In case of parameterized types, the type parameters are included in the signature.
-  -- For example, for @'PostgresqlTypes.Types.Bpchar.Bpchar' 10@, the signature will be @bpchar(10)@.
+  --
+  -- Examples:
+  --
+  -- - @int8@
+  -- - @bpchar(10)@
+  -- - @"char"@
   typeSignature :: Tagged a Text
   typeSignature =
     let params = untag (typeParams @a)
@@ -52,20 +57,26 @@
                     ]
                 )
 
-  -- | Encode the value in PostgreSQL binary format.
-  binaryEncoder :: a -> Write.Write
-
-  -- | Decode the value from PostgreSQL binary format.
-  binaryDecoder :: PtrPeeker.Variable (Either DecodingError a)
-
   -- | Represent the value in PostgreSQL textual format.
   textualEncoder :: a -> TextBuilder.TextBuilder
 
   -- | Decode the value from PostgreSQL textual format.
   textualDecoder :: Attoparsec.Parser a
 
+-- | Evidence that a type has a PostgreSQL binary wire format.
+--
+-- Not every PostgreSQL type supports binary transmission — some only have
+-- textual @send@\/@receive@ functions registered on the server. The absence
+-- of an instance of this class signals that the type is textual-only.
+class (IsPrimitive a) => IsBinaryPrimitive a where
+  -- | Encode the value in PostgreSQL binary format.
+  binaryEncoder :: a -> Write.Write
+
+  -- | Decode the value from PostgreSQL binary format.
+  binaryDecoder :: PtrPeeker.Variable (Either DecodingError a)
+
 -- | Evidence that a type can be used as an element of a PostgreSQL range type.
-class (IsScalar a, Ord a) => IsRangeElement a where
+class (IsPrimitive a, Ord a) => IsRangeElement a where
   -- | PostgreSQL range type name.
   rangeTypeName :: Tagged a Text