diff --git a/modules/services/window-managers/i3-sway/sway.nix b/modules/services/window-managers/i3-sway/sway.nix
index 1be02659..c6c5904a 100644
--- a/modules/services/window-managers/i3-sway/sway.nix
+++ b/modules/services/window-managers/i3-sway/sway.nix
@@ -269,8 +269,9 @@ let
     checkPhase = lib.optionalString cfg.checkConfig ''
       export DBUS_SESSION_BUS_ADDRESS=/dev/null
       export XDG_RUNTIME_DIR=$(mktemp -d)
+      cp "$target" sway.conf
       ${cfg.preCheckConfig}
-      ${pkgs.xvfb-run}/bin/xvfb-run ${swayPackage}/bin/sway --config "$target" --validate --unsupported-gpu
+      ${pkgs.xvfb-run}/bin/xvfb-run ${swayPackage}/bin/sway --config sway.conf --validate --unsupported-gpu
     '';
 
     text = concatStringsSep "\n"
@@ -483,12 +484,15 @@ in {
       type = types.lines;
       default = "";
       example = ''
+        sed 's/foo/bar/g' -i sway.conf
         export HOME=$(mktemp -d)
         touch ~/background.png
       '';
       description = ''
         Script to run before running `sway --validate` on the generated config
-        file. Only used if `checkConfig = true`.
+        file. The config file is available as `sway.conf`, and can be
+        manipulated without affecting the build output. Only used if
+        `checkConfig = true`.
       '';
     };
 
diff --git a/tests/modules/services/window-managers/sway/sway-check-config-precheck.nix b/tests/modules/services/window-managers/sway/sway-check-config-precheck.nix
index a7aeb1b9..77ae2f1d 100644
--- a/tests/modules/services/window-managers/sway/sway-check-config-precheck.nix
+++ b/tests/modules/services/window-managers/sway/sway-check-config-precheck.nix
@@ -6,12 +6,15 @@ lib.mkIf config.test.enableBig {
     checkConfig = true;
     preCheckConfig = ''
       export HOME=$(mktemp -d)
-      touch ~/mybg.png
+      sed 's/mybg/otherbg/g' -i sway.conf
+      touch ~/otherbg.png
     '';
     config.output."*".background = "~/mybg.png fill";
   };
 
   nmt.script = ''
     assertFileExists home-files/.config/sway/config
+    assertFileRegex home-files/.config/sway/config 'mybg\.png'
+    assertFileNotRegex home-files/.config/sway/config 'otherbg\.png'
   '';
 }