diff --git a/scripts/fetch-herdr-annotate.ps1 b/scripts/fetch-herdr-annotate.ps1
index 08cdc3f..4eaff10 100644
--- a/scripts/fetch-herdr-annotate.ps1
+++ b/scripts/fetch-herdr-annotate.ps1
@@ -35,6 +35,27 @@ if ($env:HERDR_ANNOTATE_BIN) {
   exit 0
 }
 
+# .NET rather than Get-FileHash: in Windows PowerShell 5.1, Get-FileHash is a script function of
+# Microsoft.PowerShell.Utility, not a compiled cmdlet. A powershell.exe started by a process that
+# came from PowerShell 7 inherits a PSModulePath listing PowerShell 7's modules first, loads that
+# Core-only Utility manifest instead, and Get-FileHash does not exist. SHA256 from .NET is the
+# same in 5.1 and 7 whatever the module path says.
+function Get-Sha256Hex {
+  param([Parameter(Mandatory = $true)][string]$LiteralPath)
+
+  $stream = [System.IO.File]::OpenRead($LiteralPath)
+  try {
+    $sha256 = [System.Security.Cryptography.SHA256]::Create()
+    try {
+      [System.BitConverter]::ToString($sha256.ComputeHash($stream)).Replace("-", "").ToLowerInvariant()
+    } finally {
+      $sha256.Dispose()
+    }
+  } finally {
+    $stream.Dispose()
+  }
+}
+
 $architecture = [System.Runtime.InteropServices.RuntimeInformation]::OSArchitecture.ToString()
 $target = switch ($architecture) {
   "X64" { "x86_64-pc-windows-msvc" }
@@ -51,7 +72,7 @@ try {
   $line = Get-Content -LiteralPath (Join-Path $temporary "SHA256SUMS") | Where-Object { $_ -match "\s$([regex]::Escape($asset))$" } | Select-Object -First 1
   if (-not $line) { throw "$asset is not listed in $base/SHA256SUMS" }
   $expected = ($line -split "\s+")[0].ToLowerInvariant()
-  $actual = (Get-FileHash -Algorithm SHA256 -LiteralPath (Join-Path $temporary $asset)).Hash.ToLowerInvariant()
+  $actual = Get-Sha256Hex -LiteralPath (Join-Path $temporary $asset)
   if ($actual -ne $expected) { throw "sha256 mismatch for ${asset}: expected $expected, got $actual" }
   Copy-Item -Force -LiteralPath (Join-Path $temporary $asset) -Destination "$destination.tmp"
   Move-Item -Force -LiteralPath "$destination.tmp" -Destination $destination
diff --git a/scripts/fetch-plannotator-tui.ps1 b/scripts/fetch-plannotator-tui.ps1
index 79a4ac8..3851834 100644
--- a/scripts/fetch-plannotator-tui.ps1
+++ b/scripts/fetch-plannotator-tui.ps1
@@ -114,6 +114,27 @@ function Install-PlannotatorTui {
   }
 }
 
+# .NET rather than Get-FileHash: in Windows PowerShell 5.1, Get-FileHash is a script function of
+# Microsoft.PowerShell.Utility, not a compiled cmdlet. A powershell.exe started by a process that
+# came from PowerShell 7 inherits a PSModulePath listing PowerShell 7's modules first, loads that
+# Core-only Utility manifest instead, and Get-FileHash does not exist. SHA256 from .NET is the
+# same in 5.1 and 7 whatever the module path says.
+function Get-Sha256Hex {
+  param([Parameter(Mandatory = $true)][string]$LiteralPath)
+
+  $stream = [System.IO.File]::OpenRead($LiteralPath)
+  try {
+    $sha256 = [System.Security.Cryptography.SHA256]::Create()
+    try {
+      [System.BitConverter]::ToString($sha256.ComputeHash($stream)).Replace("-", "").ToLowerInvariant()
+    } finally {
+      $sha256.Dispose()
+    }
+  } finally {
+    $stream.Dispose()
+  }
+}
+
 if ($hasLocalOverride) {
   if (-not (Test-Path -LiteralPath $localOverride -PathType Leaf)) {
     throw "PLANNOTATOR_TUI_BIN is not a file: $localOverride"
@@ -166,7 +187,7 @@ try {
     }
     $checksumFields = $matches[0].Trim() -split "\s+"
     $expected = $checksumFields[0].ToLowerInvariant()
-    $actual = (Get-FileHash -Algorithm SHA256 -LiteralPath $downloadedAsset).Hash.ToLowerInvariant()
+    $actual = Get-Sha256Hex -LiteralPath $downloadedAsset
     if ($actual -ne $expected) {
       throw "sha256 mismatch for ${asset}: expected $expected, got $actual"
     }
diff --git a/scripts/test-windows-full-manifest.py b/scripts/test-windows-full-manifest.py
index 82c33c0..d13fda2 100644
--- a/scripts/test-windows-full-manifest.py
+++ b/scripts/test-windows-full-manifest.py
@@ -109,6 +109,11 @@
         "stage-plannotator-tui.ps1",
     ],
 ]
+# The Windows builds run under powershell.exe 5.1, where Get-FileHash is a script function of
+# Microsoft.PowerShell.Utility. Started from a PowerShell 7 session, 5.1 inherits a PSModulePath
+# that loads PowerShell 7's Core-only Utility manifest instead and Get-FileHash is missing, so the
+# fetchers hash with .NET.
+WINDOWS_FETCHERS = ["scripts/fetch-herdr-annotate.ps1", "scripts/fetch-plannotator-tui.ps1"]
 
 
 def fail(path: Path, message: str) -> None:
@@ -218,6 +223,17 @@ def check_distributed(path: Path, version_path: Path, native_version_path: Path)
     check_no_link_capture(path, manifest)
 
 
+def check_windows_fetchers(root: Path) -> None:
+    for relative in WINDOWS_FETCHERS:
+        path = root / relative
+        text = path.read_text(encoding="utf-8")
+        for number, line in enumerate(text.splitlines(), 1):
+            if "Get-FileHash" in line.split("#", 1)[0]:
+                fail(path, f"line {number} calls Get-FileHash, which 5.1 may not have")
+        if "Get-Sha256Hex -LiteralPath" not in text:
+            fail(path, "the download is not checked with Get-Sha256Hex")
+
+
 def check_development(path: Path) -> None:
     manifest = load(path)
     check_top_level_windows(path, manifest)
@@ -411,6 +427,7 @@ def main() -> None:
         root / "windows-full" / "herdr-plugin.toml",
         root / "herdr-plugin.toml",
     )
+    check_windows_fetchers(root)
     lite = root / "lite" / "herdr-plugin.toml"
     check_no_link_capture(lite, load(lite))
     check_links(root / "links" / "herdr-plugin.toml", root / "herdr-plugin.toml")