diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,13 @@
 # Changelog
 
+## [0.3.0.1] - 2025-07-09
+
+* Fix discriminated union OpenAPI schema generation (see #61 for more info)
+
+## [0.3.0.0] - 2024-07-29
+
+* Dropped support for orphan instances.
+
 ## [0.2.1.4] - 2024-07-29
 
 * Non-orphan version of the `ToSchema` deriving.
diff --git a/autodocodec-openapi3.cabal b/autodocodec-openapi3.cabal
--- a/autodocodec-openapi3.cabal
+++ b/autodocodec-openapi3.cabal
@@ -1,11 +1,11 @@
 cabal-version: 1.12
 
--- This file has been generated from package.yaml by hpack version 0.36.0.
+-- This file has been generated from package.yaml by hpack version 0.36.1.
 --
 -- see: https://github.com/sol/hpack
 
 name:           autodocodec-openapi3
-version:        0.2.1.4
+version:        0.3.0.1
 synopsis:       Autodocodec interpreters for openapi3
 homepage:       https://github.com/NorfairKing/autodocodec#readme
 bug-reports:    https://github.com/NorfairKing/autodocodec/issues
@@ -27,7 +27,6 @@
   exposed-modules:
       Autodocodec.OpenAPI
       Autodocodec.OpenAPI.DerivingVia
-      Autodocodec.OpenAPI.DerivingVia.NonOrphan
       Autodocodec.OpenAPI.Schema
   other-modules:
       Paths_autodocodec_openapi3
diff --git a/src/Autodocodec/OpenAPI/DerivingVia.hs b/src/Autodocodec/OpenAPI/DerivingVia.hs
--- a/src/Autodocodec/OpenAPI/DerivingVia.hs
+++ b/src/Autodocodec/OpenAPI/DerivingVia.hs
@@ -1,26 +1,18 @@
 {-# LANGUAGE ScopedTypeVariables #-}
-{-# OPTIONS_GHC -fno-warn-orphans #-}
 
 module Autodocodec.OpenAPI.DerivingVia where
 
-import Autodocodec (Autodocodec, HasCodec)
+import Autodocodec.Class (HasCodec)
 import Autodocodec.OpenAPI.Schema (declareNamedSchemaViaCodec)
 import qualified Data.OpenApi as OpenAPI
 import Data.Proxy (Proxy (Proxy))
 import Data.Typeable (Typeable)
 
+newtype AutodocodecOpenApi a = AutodocodecOpenApi {unAutodocodecSwagger :: a}
+
 -- | An instance for 'Autodocodec' that lets you use 'DerivingVia' to derive 'OpenAPI.ToSchema' if your type has a 'HasCodec' instance.
 --
 -- > deriving (OpenAPI.ToSchema) via (Autodocodec FooBar)
-instance (Typeable a, HasCodec a) => OpenAPI.ToSchema (Autodocodec a) where
-  -- This is declared like this as because now 'declareNamedSchema' takes no arguments, it can be memoized (like a top level variable is).
-  -- As a result, the result of the 'let', that is the schema, should also be memoized,
-  -- so with this definition schema in 'declaredNamedSchema' should only need to be calculated once IF the instance is of the form:
-  -- > deriving (OpenAPI.ToSchema) via (Autodocodec FooBar)
-  -- where FooBar is a concrete type.
-  -- If the instance is of the form:
-  -- > deriving via (Autodocodec (FooBar a)) instance (OpenAPI.ToSchema (FooBar a))
-  -- this memoisation trick probably won't work (as 'declaredNamedSchema' actually is a function due to hiddent typeclass dictionary arguments)
-  -- but it shouldn't hurt to try. See:
-  -- https://stackoverflow.com/questions/77056264/caching-an-expensive-to-compute-result-in-a-class-instance
+instance (Typeable a, HasCodec a) => OpenAPI.ToSchema (AutodocodecOpenApi a) where
+  -- See comments in 'Autodocodec.OpenAPI.DerivingVia' for the reason why this is defined like this.
   declareNamedSchema = let schema = declareNamedSchemaViaCodec (Proxy :: Proxy a) in const schema
diff --git a/src/Autodocodec/OpenAPI/DerivingVia/NonOrphan.hs b/src/Autodocodec/OpenAPI/DerivingVia/NonOrphan.hs
deleted file mode 100644
--- a/src/Autodocodec/OpenAPI/DerivingVia/NonOrphan.hs
+++ /dev/null
@@ -1,18 +0,0 @@
-{-# LANGUAGE ScopedTypeVariables #-}
-
-module Autodocodec.OpenAPI.DerivingVia.NonOrphan where
-
-import Autodocodec.Class (HasCodec)
-import Autodocodec.OpenAPI.Schema (declareNamedSchemaViaCodec)
-import qualified Data.OpenApi as OpenAPI
-import Data.Proxy (Proxy (Proxy))
-import Data.Typeable (Typeable)
-
-newtype AutodocodecOpenApi a = AutodocodecOpenApi {unAutodocodecSwagger :: a}
-
--- | An instance for 'Autodocodec' that lets you use 'DerivingVia' to derive 'OpenAPI.ToSchema' if your type has a 'HasCodec' instance.
---
--- > deriving (OpenAPI.ToSchema) via (Autodocodec FooBar)
-instance (Typeable a, HasCodec a) => OpenAPI.ToSchema (AutodocodecOpenApi a) where
-  -- See comments in 'Autodocodec.OpenAPI.DerivingVia' for the reason why this is defined like this.
-  declareNamedSchema = let schema = declareNamedSchemaViaCodec (Proxy :: Proxy a) in const schema
diff --git a/src/Autodocodec/OpenAPI/Schema.hs b/src/Autodocodec/OpenAPI/Schema.hs
--- a/src/Autodocodec/OpenAPI/Schema.hs
+++ b/src/Autodocodec/OpenAPI/Schema.hs
@@ -6,7 +6,6 @@
 {-# LANGUAGE OverloadedStrings #-}
 {-# LANGUAGE RecordWildCards #-}
 {-# LANGUAGE ScopedTypeVariables #-}
-{-# OPTIONS_GHC -fno-warn-orphans #-}
 
 module Autodocodec.OpenAPI.Schema where
 
@@ -195,7 +194,7 @@
         let d =
               Discriminator
                 { _discriminatorPropertyName = pn,
-                  _discriminatorMapping = InsOrdHashMap.fromHashMap $ fmap fst m
+                  _discriminatorMapping = InsOrdHashMap.fromHashMap $ fmap (\x -> "#/components/schemas/" <> fst x) m
                 }
             mkSchema dName (refName, oc) = do
               s <- goObject $ oc *> (requiredFieldWith' pn (literalTextCodec dName) .= const dName)