diff --git a/pkgs/by-name/pl/playwright-mcp/package.nix b/pkgs/by-name/pl/playwright-mcp/package.nix
index 09c30c7890af..e91874fbb6d2 100644
--- a/pkgs/by-name/pl/playwright-mcp/package.nix
+++ b/pkgs/by-name/pl/playwright-mcp/package.nix
@@ -32,7 +32,8 @@ buildNpmPackage rec {
 
     wrapProgram $out/bin/playwright-mcp \
       --set PLAYWRIGHT_BROWSERS_PATH ${playwright-driver.browsers} \
-      --set-default PLAYWRIGHT_MCP_BROWSER chromium
+      --set-default PLAYWRIGHT_MCP_BROWSER chromium \
+      --run 'if [ -z "$PLAYWRIGHT_MCP_USER_DATA_DIR" ]; then export PLAYWRIGHT_MCP_ISOLATED=1; fi'
   '';
 
   dontNpmBuild = true;