diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -15,3 +15,6 @@
 
 0.4.1.0, released 2025-12-02
     Publish to Hackage
+
+0.4.1.1, 2026-03-22
+    Add flake.nix for development environment
diff --git a/Makefile b/Makefile
--- a/Makefile
+++ b/Makefile
@@ -7,6 +7,10 @@
 package: package.yaml
 	hpack
 
+.PHONY: develop
+develop:  ## Enter development environment
+	nix develop
+
 .PHONY: freeze
 freeze:  ## Freeze dependencies
 	cabal freeze
@@ -43,6 +47,10 @@
 release:  ## release build (no debug symbols, etc).
 	cabal build --enable-executable-stripping all
 	cabal list-bin "$(PROJECT)-exe"
+
+.PHONY: release-nix
+release-nix: ## Release build for Nix
+	nix build .#default --print-build-logs
 
 .PHONY: check
 check:  ## runs cabal check
diff --git a/cabal.project b/cabal.project
--- a/cabal.project
+++ b/cabal.project
@@ -1,5 +1,7 @@
 packages: .
           
+constraints: crypton ==1.0.4
+          
 source-repository-package
   type: git
   location: https://github.com/bitnomial/bitcoin-compact-filters
diff --git a/haskell-opentimestamps-client.cabal b/haskell-opentimestamps-client.cabal
--- a/haskell-opentimestamps-client.cabal
+++ b/haskell-opentimestamps-client.cabal
@@ -1,11 +1,11 @@
 cabal-version: 1.12
 
--- This file has been generated from package.yaml by hpack version 0.38.2.
+-- This file has been generated from package.yaml by hpack version 0.38.3.
 --
 -- see: https://github.com/sol/hpack
 
 name:           haskell-opentimestamps-client
-version:        0.4.1.0
+version:        0.4.1.1
 synopsis:       Haskell implementation of a basic OpenTimestamps client
 description:    Please see the README on Codeberg at <https://codeberg.org/photonsphere/haskell-opentimestamps-client#readme>
 category:       Bitcoin, Finance, Network, Cryptography
@@ -36,13 +36,13 @@
   ghc-options: -Wall -Wcompat -Widentities -Wincomplete-record-updates -Wincomplete-uni-patterns -Wmissing-export-lists -Wmissing-home-modules -Wpartial-fields -Wredundant-constraints
   build-depends:
       base >=4.7 && <5
-    , base16 >=0.1 && <2.0
+    , base16 >=0.1 && <2
     , bytestring >=0.10 && <0.13
     , containers >=0.5 && <0.8
     , cryptonite >=0.25 && <0.35
     , directory >=1.2 && <1.4
     , filepath >=1.3 && <1.5
-    , haskell-opentimestamps >=0.5.5.0 && <1.0
+    , haskell-opentimestamps >=0.5.5.0 && <1
     , memory >=0.14 && <0.19
     , temporary >=1.2 && <1.4
     , text >=1.2 && <2.2
diff --git a/package.yaml b/package.yaml
--- a/package.yaml
+++ b/package.yaml
@@ -1,5 +1,5 @@
 name:                haskell-opentimestamps-client
-version:             0.4.1.0
+version:             0.4.1.1
 license:             BSD3
 #x-license:           BSD-3-Clause OR Apache-2.0
 author:              "A.H.M. (Mari) Donkers"
@@ -37,12 +37,12 @@
     - cryptonite >= 0.25 && < 0.35
     - directory >= 1.2 && < 1.4
     - filepath >= 1.3 && < 1.5
-    - haskell-opentimestamps >= 0.5.5.0 && < 1.0
+    - haskell-opentimestamps >= 0.5.5.0 && < 1
     - memory >= 0.14 && < 0.19
     - temporary >= 1.2 && < 1.4
     - text >= 1.2 && < 2.2
     - time >= 1.4 && < 1.13
-    - base16 >= 0.1 && < 2.0
+    - base16 >= 0.1 && < 2
     - containers >= 0.5 && < 0.8
 
 executables:
