diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,6 +1,14 @@
 # Revision history for mmzk-env
 
 
+## 0.3.0.0 -- 2026-03-22
+
+* Fixed `DefaultBool` to follow the proper witness pattern:
+  * Changed from a newtype with `TypeParser` to a phantom type with `TypeParserW`.
+  * Added second type parameter (consistent with `DefaultNum` and `DefaultString`) enabling use with the `Di` type alias.
+* `DefaultBool` now accepts `True`, `False`, `true`, `false`, `T`, `F`, `t`, `f`, `1`, `0`.
+
+
 ## 0.2.1.1 -- 2026-03-22
 
 * Added `DefaultBool` for `Bool` fields with a type-level default value.
diff --git a/mmzk-env.cabal b/mmzk-env.cabal
--- a/mmzk-env.cabal
+++ b/mmzk-env.cabal
@@ -1,6 +1,6 @@
 cabal-version:      2.4
 name:               mmzk-env
-version:            0.2.1.1
+version:            0.3.0.0
 
 synopsis:           Read environment variables into a user-defined data type
 description:
@@ -51,13 +51,13 @@
     import:           settings
     exposed-modules:
         Data.Env
-        Data.Env.DefaultBool
         Data.Env.EnumParser
         Data.Env.ExtractFields
         Data.Env.RecordParser
         Data.Env.RecordParserW
         Data.Env.TypeParser
         Data.Env.TypeParserW
+        Data.Env.Witness.DefaultBool
         Data.Env.Witness.DefaultNum
         Data.Env.Witness.DefaultString
     build-depends:
diff --git a/src/Data/Env/DefaultBool.hs b/src/Data/Env/DefaultBool.hs
deleted file mode 100644
--- a/src/Data/Env/DefaultBool.hs
+++ /dev/null
@@ -1,43 +0,0 @@
--- |
--- Module: Data.Env.DefaultBool
--- Description: A helper type for Bool fields with a type-level default value.
---
--- This module provides 'DefaultBool', a newtype wrapping 'Bool' whose
--- 'TypeParser' instance returns a type-level default when the input is empty.
---
--- Example usage:
---
--- > data Config = Config
--- >   { debug   :: DefaultBool 'False
--- >   , verbose :: DefaultBool 'True
--- >   } deriving (Show, Generic, EnvSchema)
--- >
--- > -- DEBUG unset → DefaultBool False
--- > -- DEBUG=True  → DefaultBool True
--- > -- DEBUG=False → DefaultBool False
-module Data.Env.DefaultBool where
-
-import Data.Env.TypeParser (TypeParser(..))
-import Data.Proxy          (Proxy(..))
-
--- | A 'Bool' field with a type-level default.
---
--- When the environment variable is absent (empty string) the field takes the
--- value @def@; otherwise the string is parsed as a regular 'Bool'.
-newtype DefaultBool (def :: Bool) = DefaultBool Bool
-  deriving (Show, Eq, Ord)
-
--- | Reflect a type-level 'Bool' to a value-level 'Bool'.
-class BoolDefault (b :: Bool) where
-  boolDefault :: Proxy b -> Bool
-
-instance BoolDefault 'True where
-  boolDefault _ = True
-
-instance BoolDefault 'False where
-  boolDefault _ = False
-
-instance BoolDefault def => TypeParser (DefaultBool def) where
-  parseType "" = Right (DefaultBool (boolDefault (Proxy :: Proxy def)))
-  parseType s  = DefaultBool <$> parseType s
-  {-# INLINE parseType #-}
diff --git a/src/Data/Env/Witness/DefaultBool.hs b/src/Data/Env/Witness/DefaultBool.hs
new file mode 100644
--- /dev/null
+++ b/src/Data/Env/Witness/DefaultBool.hs
@@ -0,0 +1,62 @@
+{-# LANGUAGE MultiParamTypeClasses #-}
+
+{- |
+Witness type for parsing 'Bool' with a type-level default value.
+-}
+module Data.Env.Witness.DefaultBool (
+  DefaultBool,
+) where
+
+import Data.Env.TypeParser
+import Data.Env.TypeParserW
+import Data.Proxy
+
+-- | Witness type for parsing 'Bool' with a default value.
+--
+-- The type parameter @b@ is a type-level 'Bool' that specifies the default
+-- value used when the environment variable is absent (empty string).
+-- The type parameter @a@ is the parsed type (always 'Bool').
+--
+-- ==== __Examples__
+--
+-- >>> parseTypeW (Proxy @(DefaultBool 'False Bool)) ""
+-- Right False
+--
+-- >>> parseTypeW (Proxy @(DefaultBool 'True Bool)) ""
+-- Right True
+--
+-- >>> parseTypeW (Proxy @(DefaultBool 'False Bool)) "True"
+-- Right True
+--
+-- >>> parseTypeW' (Proxy @(DefaultBool 'False Bool)) "invalid"
+-- Nothing
+data DefaultBool (b :: Bool) a
+
+class BoolVal (b :: Bool) where
+  boolVal :: Proxy b -> Bool
+
+instance BoolVal 'True where
+  boolVal _ = True
+
+instance BoolVal 'False where
+  boolVal _ = False
+
+-- | Parse a 'Bool' with a default fallback.
+--
+-- When the input string is empty, returns the default value specified by the
+-- type-level 'Bool' @b@. Otherwise, attempts to parse the string as 'Bool',
+-- accepting @True@, @False@, @true@, @false@, @T@, @F@, @t@, @f@, @1@, @0@.
+instance BoolVal b => TypeParserW (DefaultBool b Bool) Bool where
+  parseTypeW :: Proxy (DefaultBool b Bool) -> String -> Either String Bool
+  parseTypeW _ str = case str of
+    ""      -> Right (boolVal (Proxy :: Proxy b))
+    "true"  -> Right True
+    "false" -> Right False
+    "T"     -> Right True
+    "F"     -> Right False
+    "t"     -> Right True
+    "f"     -> Right False
+    "1"     -> Right True
+    "0"     -> Right False
+    _       -> parseType str
+  {-# INLINE parseTypeW #-}
diff --git a/test/DefaultBoolSpec.hs b/test/DefaultBoolSpec.hs
--- a/test/DefaultBoolSpec.hs
+++ b/test/DefaultBoolSpec.hs
@@ -1,23 +1,33 @@
 module DefaultBoolSpec ( spec ) where
 
 import Data.Either ( isLeft )
-import Data.Env.DefaultBool
-import Data.Env.TypeParser
+import Data.Env.TypeParserW
+import Data.Env.Witness.DefaultBool
+import Data.Proxy
 import Test.Hspec
 
 spec :: Spec
 spec = describe "DefaultBool" do
-  it "parses True" do
-    parseType @(DefaultBool 'False) "True" `shouldBe` Right (DefaultBool True)
-    parseType @(DefaultBool 'True)  "True" `shouldBe` Right (DefaultBool True)
-  it "parses False" do
-    parseType @(DefaultBool 'False) "False" `shouldBe` Right (DefaultBool False)
-    parseType @(DefaultBool 'True)  "False" `shouldBe` Right (DefaultBool False)
   it "defaults to False when empty" do
-    parseType @(DefaultBool 'False) "" `shouldBe` Right (DefaultBool False)
+    parseTypeW (Proxy @(DefaultBool 'False Bool)) "" `shouldBe` Right False
   it "defaults to True when empty" do
-    parseType @(DefaultBool 'True) "" `shouldBe` Right (DefaultBool True)
+    parseTypeW (Proxy @(DefaultBool 'True Bool)) "" `shouldBe` Right True
+  it "parses True / False" do
+    parseTypeW (Proxy @(DefaultBool 'False Bool)) "True"  `shouldBe` Right True
+    parseTypeW (Proxy @(DefaultBool 'False Bool)) "False" `shouldBe` Right False
+  it "parses true / false" do
+    parseTypeW (Proxy @(DefaultBool 'False Bool)) "true"  `shouldBe` Right True
+    parseTypeW (Proxy @(DefaultBool 'False Bool)) "false" `shouldBe` Right False
+  it "parses T / F" do
+    parseTypeW (Proxy @(DefaultBool 'False Bool)) "T" `shouldBe` Right True
+    parseTypeW (Proxy @(DefaultBool 'False Bool)) "F" `shouldBe` Right False
+  it "parses t / f" do
+    parseTypeW (Proxy @(DefaultBool 'False Bool)) "t" `shouldBe` Right True
+    parseTypeW (Proxy @(DefaultBool 'False Bool)) "f" `shouldBe` Right False
+  it "parses 1 / 0" do
+    parseTypeW (Proxy @(DefaultBool 'False Bool)) "1" `shouldBe` Right True
+    parseTypeW (Proxy @(DefaultBool 'False Bool)) "0" `shouldBe` Right False
   it "fails to parse other values" do
-    parseType @(DefaultBool 'False) "1"     `shouldSatisfy` isLeft
-    parseType @(DefaultBool 'False) "true"  `shouldSatisfy` isLeft
-    parseType @(DefaultBool 'False) "false" `shouldSatisfy` isLeft
+    parseTypeW (Proxy @(DefaultBool 'False Bool)) "yes"     `shouldSatisfy` isLeft
+    parseTypeW (Proxy @(DefaultBool 'False Bool)) "no"      `shouldSatisfy` isLeft
+    parseTypeW (Proxy @(DefaultBool 'False Bool)) "invalid" `shouldSatisfy` isLeft
diff --git a/test/RecordParserWSpec.hs b/test/RecordParserWSpec.hs
--- a/test/RecordParserWSpec.hs
+++ b/test/RecordParserWSpec.hs
@@ -11,6 +11,7 @@
 import Data.Map qualified as M
 import GHC.Generics
 import Test.Hspec
+import Data.Env.Witness.DefaultBool (DefaultBool)
 
 data NameW
 
@@ -23,9 +24,10 @@
 
 
 data Config c = Config
-  { port :: Di (DefaultNum 5432) c Int
-  , env  :: Di Solo c String
-  , name :: Column c NameW String
+  { port  :: Di (DefaultNum 5432) c Int
+  , env   :: Di Solo c String
+  , name  :: Column c NameW String
+  , debug :: Di (DefaultBool 'False) c Bool
   }
   deriving (Generic)
 
@@ -34,15 +36,18 @@
 
 spec :: Spec
 spec = describe "parseRecordW for Config" do
-  it "uses default port 5432 when port not specified" do
+  it "uses default port 5432 and default debug False when not specified" do
     let envMap = M.fromList [("env", "production"), ("name", "name")]
-    parseRecordW @(Config 'Dec) envMap `shouldBe` Right (Config 5432 "production" "name")
-  it "parses config with custom port" do
-    let envMap = M.fromList [("port", "8080"), ("env", "development"), ("name", "name")]
-    parseRecordW @(Config 'Dec) envMap `shouldBe` Right (Config 8080 "development" "name")
+    parseRecordW @(Config 'Dec) envMap `shouldBe` Right (Config 5432 "production" "name" False)
+  it "parses config with custom port and explicit debug" do
+    let envMap = M.fromList [("port", "8080"), ("env", "development"), ("name", "name"), ("debug", "True")]
+    parseRecordW @(Config 'Dec) envMap `shouldBe` Right (Config 8080 "development" "name" True)
   it "fails to parse invalid port value" do
     let envMap = M.fromList [("port", "not-a-number"), ("env", "test"), ("name", "name")]
     parseRecordW @(Config 'Dec) envMap `shouldSatisfy` isLeft
   it "fails to parse invalid name value" do
     let envMap = M.fromList [("env", "test"), ("name", "1234567890poiuytrewq")]
+    parseRecordW @(Config 'Dec) envMap `shouldSatisfy` isLeft
+  it "fails to parse invalid debug value" do
+    let envMap = M.fromList [("env", "test"), ("name", "name"), ("debug", "yes")]
     parseRecordW @(Config 'Dec) envMap `shouldSatisfy` isLeft