diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,6 +6,10 @@
 and this project adheres to the
 [Haskell Package Versioning Policy](https://pvp.haskell.org/).
 
+## 0.5.1.0 - 2026-07-02
+
+* Fix a regression on unsupported operating systems.
+
 ## 0.5.0.0 - 2026-06-22
 
 * Fix a regression on Linux operating systems, whereby `xdg-open` would not
diff --git a/LICENSE b/LICENSE
--- a/LICENSE
+++ b/LICENSE
@@ -1,30 +1,30 @@
-Copyright (c) 2015, rightfold
-
-All rights reserved.
-
-Redistribution and use in source and binary forms, with or without
-modification, are permitted provided that the following conditions are met:
-
-    * Redistributions of source code must retain the above copyright
-      notice, this list of conditions and the following disclaimer.
-
-    * Redistributions in binary form must reproduce the above
-      copyright notice, this list of conditions and the following
-      disclaimer in the documentation and/or other materials provided
-      with the distribution.
-
-    * Neither the name of rightfold nor the names of other
-      contributors may be used to endorse or promote products derived
-      from this software without specific prior written permission.
-
-THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
-"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
-LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
-A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
-OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
-SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
-LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
-DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
-THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
-(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
-OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+Copyright (c) 2015, rightfold
+
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are met:
+
+    * Redistributions of source code must retain the above copyright
+      notice, this list of conditions and the following disclaimer.
+
+    * Redistributions in binary form must reproduce the above
+      copyright notice, this list of conditions and the following
+      disclaimer in the documentation and/or other materials provided
+      with the distribution.
+
+    * Neither the name of rightfold nor the names of other
+      contributors may be used to endorse or promote products derived
+      from this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
diff --git a/README.md b/README.md
--- a/README.md
+++ b/README.md
@@ -1,9 +1,9 @@
-# open-browser
-
-A Haskell library that provides the function `openBrowser` that, given a URL or
-other item associated with a web browser, yields an IO action that seeks to open
-the item in the user's preferred web browser.
-
-Supported operating systems are Windows, macOS, Linux and BSD.
-
-Originally developed by rightfold.
+# open-browser
+
+A Haskell library that provides the function `openBrowser` that, given a URL or
+other item associated with a web browser, yields an IO action that seeks to open
+the item in the user's preferred web browser.
+
+Supported operating systems are Windows, macOS, Linux and BSD.
+
+Originally developed by rightfold.
diff --git a/Setup.hs b/Setup.hs
--- a/Setup.hs
+++ b/Setup.hs
@@ -1,2 +1,2 @@
-import Distribution.Simple
-main = defaultMain
+import Distribution.Simple
+main = defaultMain
diff --git a/lib/unsupported-os/Web/Browser/OS.hs b/lib/unsupported-os/Web/Browser/OS.hs
--- a/lib/unsupported-os/Web/Browser/OS.hs
+++ b/lib/unsupported-os/Web/Browser/OS.hs
@@ -10,6 +10,6 @@
      String
      -- ^ URL or other item to try to open.
   -> IO ()
-openBrowserWithExitCode =
+openBrowser _ =
   -- Operation never succeeds
   error "openBrowser: Unsupported operating system."
diff --git a/open-browser.cabal b/open-browser.cabal
--- a/open-browser.cabal
+++ b/open-browser.cabal
@@ -5,7 +5,7 @@
 -- see: https://github.com/sol/hpack
 
 name:           open-browser
-version:        0.5.0.0
+version:        0.5.1.0
 synopsis:       Open a web browser from Haskell
 description:    Open a web browser from Haskell. Windows, macOS, Linux and BSD are supported.
 category:       Web