diff --git a/bootstrap.bat b/bootstrap.bat
index 2f6065909..33adc8293 100644
--- a/bootstrap.bat
+++ b/bootstrap.bat
@@ -96,6 +96,23 @@ if "%PW_ENVIRONMENT_ROOT%"=="" (
   set "_PW_ACTUAL_ENVIRONMENT_ROOT=%PW_ENVIRONMENT_ROOT%"
 )
 
+:: Check case sensitivity.
+:: TODO: https://pwbug.dev/322437881 - Support case-sensitive filesystems on
+:: Windows.
+fsutil.exe file queryCaseSensitiveInfo "%PW_PROJECT_ROOT%" | findstr disabled > NUL
+if "%ERRORLEVEL%" == "1" (
+  echo.
+  echo Error: Your project's directory has case sensitivity enabled.
+  echo.
+  echo   Pigweed does not yet support case-sensitive file systems on Windows.
+  echo   Please run this command **FROM AN ADMINISTRATOR COMMAND PROMPT** to
+  echo   disable case sensitivity on your checkout:
+  echo.
+  echo     fsutil.exe file setCaseSensitiveInfo "%PW_PROJECT_ROOT%" disable
+  echo.
+  goto finish
+)
+
 set "shell_file=%_PW_ACTUAL_ENVIRONMENT_ROOT%\activate.bat"
 
 set "_pw_start_script=%PW_ROOT%\pw_env_setup\py\pw_env_setup\windows_env_start.py"