diff --git a/ParallelKit.Harness.ps1 b/ParallelKit.Harness.ps1
index 39bfebe..b819e97 100644
--- a/ParallelKit.Harness.ps1
+++ b/ParallelKit.Harness.ps1
@@ -180,6 +180,32 @@ $j = Start-PkProcess -FilePath $cmdExe -Arguments '/c exit 0'
 $null = Wait-PkProcess -Process $j.Proc -TimeoutMs 5000
 Test-Assert ([PkChildProcessJob]::Assign($j.Proc) -or $j.Proc.HasExited) "started processes are tied to the job object"
 $j.Proc.Dispose()
+
+# ConvertTo-PkArgumentString: exact output for the tricky cases, then a
+# round trip through a real program that prints each argument it received.
+Test-Assert ((ConvertTo-PkArgumentString @('plain', 'two words', '')) -eq 'plain "two words" ""') "arguments with spaces are quoted, empty ones become `"`""
+Test-Assert ((ConvertTo-PkArgumentString @('C:\dir with space\')) -eq '"C:\dir with space\\"') "a trailing backslash is doubled inside quotes"
+Test-Assert ((ConvertTo-PkArgumentString @('say "hi"', 'a\"b')) -eq '"say \"hi\"" "a\\\"b"') "quotes are escaped, and backslashes before them doubled"
+Test-Assert ((ConvertTo-PkArgumentString @('C:\no\spaces\')) -eq 'C:\no\spaces\') "an argument that needs no quotes is left alone"
+# Built with the .NET Framework's csc.exe (on every Windows machine) rather
+# than Add-Type, which can't build an .exe under PowerShell 7.
+$argvExe = Join-Path $env:TEMP ("pk-argv-" + [guid]::NewGuid().ToString("N") + ".exe")
+$argvSrc = [System.IO.Path]::ChangeExtension($argvExe, '.cs')
+[System.IO.File]::WriteAllText($argvSrc, 'public static class PkArgv { public static void Main(string[] args) { foreach (string a in args) { System.Console.WriteLine("[" + a + "]"); } } }')
+$cscExe = Join-Path $env:SystemRoot 'Microsoft.NET\Framework64\v4.0.30319\csc.exe'
+$csc = $null
+try { $csc = Invoke-PkProcessWithTimeout -FilePath $cscExe -Arguments (ConvertTo-PkArgumentString @('/nologo', ('/out:' + $argvExe), $argvSrc)) } catch { Write-Host "  csc.exe failed to run: $_" }
+[System.IO.File]::Delete($argvSrc)
+$compiled = ($null -ne $csc -and $csc.ExitCode -eq 0 -and [System.IO.File]::Exists($argvExe))
+Test-Assert $compiled "the argument-printing test program compiles"
+if ($compiled) {
+    $tricky = @('plain', 'two words', '', 'C:\dir with space\', 'say "hi"', 'a\"b', 'tab	here', 'x\\y', '\\server\share\')
+    $r = Invoke-PkProcessWithTimeout -FilePath $argvExe -Arguments (ConvertTo-PkArgumentString $tricky)
+    $received = @(([string]$r.Stdout).Split([string[]]@("`r`n"), [System.StringSplitOptions]::RemoveEmptyEntries))
+    $expected = @($tricky | ForEach-Object { "[" + $_ + "]" })
+    Test-Assert (($received -join '|') -eq ($expected -join '|')) ("a program receives exactly the arguments given (got " + ($received -join ' ') + ")")
+    try { [System.IO.File]::Delete($argvExe) } catch { }  # temp file only; best effort
+}
 Write-Host ""
 
 # ==============================================================================
diff --git a/ParallelKit.ps1 b/ParallelKit.ps1
index b4aa176..8319880 100644
--- a/ParallelKit.ps1
+++ b/ParallelKit.ps1
@@ -517,6 +517,50 @@ function Invoke-PkRun {
 #  External processes (all raw .NET - safe inside workers)
 # ==============================================================================
 
+function ConvertTo-PkArgumentString {
+    # Joins arguments into one command line, quoting each so a program sees
+    # exactly that list: an argument with a space, tab, newline or quote is
+    # wrapped in quotes, its quotes become \", and backslashes are doubled
+    # where they come before a quote. These are the C runtime's rules, which
+    # most Windows programs use (cmd.exe's own parsing is different).
+    # .NET Framework's ProcessStartInfo has no ArgumentList, hence this.
+    #   ConvertTo-PkArgumentString @($in, '-o', $out)  ->  "C:\My Files\a.png" -o C:\out\a.jxl
+    param(
+        [Parameter(Mandatory, Position = 0)]
+        [AllowEmptyCollection()]
+        [AllowEmptyString()]
+        [string[]]$Arguments
+    )
+    $parts = [System.Collections.Generic.List[string]]::new()
+    foreach ($arg in $Arguments) {
+        if ($null -eq $arg) { $arg = '' }
+        if ($arg.Length -gt 0 -and $arg.IndexOfAny([char[]]@(' ', "`t", "`n", "`v", '"')) -lt 0) {
+            $parts.Add($arg)
+            continue
+        }
+        $sb = [System.Text.StringBuilder]::new()
+        $null = $sb.Append('"')
+        $backslashes = 0
+        foreach ($ch in $arg.ToCharArray()) {
+            if ($ch -eq '\') { $backslashes++; continue }
+            if ($ch -eq '"') {
+                # Each backslash before a quote is doubled, then the quote escaped.
+                $null = $sb.Append('\', 2 * $backslashes + 1)
+                $null = $sb.Append('"')
+            } else {
+                if ($backslashes -gt 0) { $null = $sb.Append('\', $backslashes) }
+                $null = $sb.Append($ch)
+            }
+            $backslashes = 0
+        }
+        # Trailing backslashes are doubled so they don't escape the closing quote.
+        if ($backslashes -gt 0) { $null = $sb.Append('\', 2 * $backslashes) }
+        $null = $sb.Append('"')
+        $parts.Add($sb.ToString())
+    }
+    return ($parts -join ' ')
+}
+
 function Start-PkProcess {
     # Starts a hidden child process with stdout/stderr redirected and being
     # read asynchronously (so a chatty process can't block on a full pipe).
@@ -1224,7 +1268,7 @@ function Get-PkWorkerSafeFunctionNames {
     return @('Write-PkMessage', 'Test-PkAbortSignal', 'Test-PkCancelRequested', 'Initialize-PkThreadPool',
              'Start-PkProcess', 'Wait-PkProcess', 'Complete-PkProcess', 'Invoke-PkProcessWithTimeout',
              'Invoke-PkProcessDispatch', 'Invoke-PkProcessDispatchCore', 'Invoke-PkProcessBatch',
-             'Register-PkCancellationSource', 'Unregister-PkCancellationSource')
+             'Register-PkCancellationSource', 'Unregister-PkCancellationSource', 'ConvertTo-PkArgumentString')
 }
 
 function Receive-PkCompletedHandles {
diff --git a/README.md b/README.md
index 8452e2d..b8a82ce 100644
--- a/README.md
+++ b/README.md
@@ -23,7 +23,7 @@ Most uses are this: a list of command-line programs, run a few at a time, where
 . "$PSScriptRoot\ParallelKit.ps1"
 
 $commands = foreach ($f in Get-ChildItem *.png) {
-    @{ FilePath = 'cjxl.exe'; Arguments = ('"{0}" "{0}.jxl"' -f $f.FullName) }
+    @{ FilePath = 'cjxl.exe'; Arguments = (ConvertTo-PkArgumentString @($f.FullName, "$($f.FullName).jxl")) }
 }
 $batch = Invoke-PkRun { Invoke-PkProcessBatch -Commands $commands -MaxConcurrent 6 }
 
@@ -102,7 +102,7 @@ Each public function has a comment block at the top of its definition in `Parall
 ```powershell
 # Any command-line tool works. cjxl is a JPEG XL image encoder.
 $commands = foreach ($f in Get-ChildItem *.png) {
-    @{ FilePath = 'cjxl.exe'; Arguments = ('"{0}" "{0}.jxl"' -f $f.FullName); Source = $f }
+    @{ FilePath = 'cjxl.exe'; Arguments = (ConvertTo-PkArgumentString @($f.FullName, "$($f.FullName).jxl")); Source = $f }
 }
 $batchParams = @{
     Commands      = $commands
@@ -117,7 +117,7 @@ $batch = Invoke-PkRun { Invoke-PkProcessBatch @batchParams }
 
 Long parameter lists in these examples use splatting (`@batchParams`) instead of trailing backticks: it's easier to read, and a stray space after a backtick can't break it.
 
-Each command is a hashtable with `FilePath`, `Arguments` and optionally `WorkingDirectory`, plus any keys of your own. `Arguments` is passed to the program as one string, exactly as written, so put quotes around paths that may contain spaces (as above). Programs run hidden, with their output captured.
+Each command is a hashtable with `FilePath`, `Arguments` and optionally `WorkingDirectory`, plus any keys of your own. `Arguments` is passed to the program as one string, exactly as written. `ConvertTo-PkArgumentString @(...)` builds that string from a list, quoting each argument so the program gets exactly that list back, spaces, quotes and trailing backslashes included. It follows the rules most Windows programs use; `cmd.exe /c` parses its own way. Programs run hidden, with their output captured.
 
 `Invoke-PkProcessBatch` returns `@{ Results; Aborted; ForceKilledCount }`. Each result is `@{ Command; ExitCode; Stdout; Stderr; StreamTimedOut; StreamError; StartError; Aborted }`, with every field always present:
 
@@ -235,6 +235,7 @@ Closures: build every callback that uses your local variables with `{ ... }.GetN
 | Function | Use |
 |---|---|
 | `Invoke-PkProcessWithTimeout -FilePath -Arguments -TimeoutMs` | Run one program and wait, with a hard time limit (default 60s). Returns `@{ ExitCode; Stdout; Stderr; StreamTimedOut; StreamError }`. If it overruns, or the run is aborted, the program is killed and this **throws**; add `-IgnoreAbort` for a cleanup step that must finish anyway. |
+| `ConvertTo-PkArgumentString @(args)` | Join a list of arguments into one correctly quoted command line, for any `-Arguments` / `Arguments` value. |
 | `Start-PkProcess -FilePath -Arguments` | Start one hidden, with output captured in the background. Returns `@{ Proc; StdoutTask; StderrTask; Stopwatch }`; throws if it can't start. |
 | `Wait-PkProcess -Process -TimeoutMs` | Wait for exit with a timeout that can't overrun. Returns `$true` if it exited. |
 | `Complete-PkProcess -Job` | Collect exit code and output from a finished one (`-Job` is what `Start-PkProcess` returned). Same result as `Invoke-PkProcessWithTimeout`. |