diff --git a/Assistant/Threads/Upgrader.hs b/Assistant/Threads/Upgrader.hs
index 4fff909203..a0e39e4174 100644
--- a/Assistant/Threads/Upgrader.hs
+++ b/Assistant/Threads/Upgrader.hs
@@ -31,7 +31,7 @@ import qualified Data.Text as T
 
 upgraderThread :: UrlRenderer -> NamedThread
 upgraderThread urlrenderer = namedThread "Upgrader" $
-	when (isJust BuildInfo.upgradelocation) $ do
+	when upgradeSupported $ do
 		{- Check for upgrade on startup, unless it was just
 		 - upgraded. -}
 		unlessM (liftIO checkSuccessfulUpgrade) $
diff --git a/Assistant/Upgrade.hs b/Assistant/Upgrade.hs
index db6f6a26e0..b61eff54c0 100644
--- a/Assistant/Upgrade.hs
+++ b/Assistant/Upgrade.hs
@@ -338,6 +338,18 @@ distributionInfoUrl = fromJust BuildInfo.upgradelocation ++ ".info"
 distributionInfoSigUrl :: String
 distributionInfoSigUrl = distributionInfoUrl ++ ".sig"
 
+{- Upgrade only supported on linux and OSX. -}
+upgradeSupported :: Bool
+#ifdef linux_HOST_OS
+upgradeSupported = isJust BuildInfo.upgradelocation
+#else
+#ifdef darwin_HOST_OS
+upgradeSupported = isJust BuildInfo.upgradelocation
+#else
+upgradeSupported = False
+#endif
+#endif
+
 {- Verifies that a file from the git-annex distribution has a valid
  - signature. Pass the detached .sig file; the file to be verified should
  - be located next to it.
diff --git a/Assistant/WebApp/Configurators/Preferences.hs b/Assistant/WebApp/Configurators/Preferences.hs
index 59ffff71a9..d92362575e 100644
--- a/Assistant/WebApp/Configurators/Preferences.hs
+++ b/Assistant/WebApp/Configurators/Preferences.hs
@@ -21,7 +21,7 @@ import Annex.NumCopies
 import Utility.DataUnits
 import Git.Config
 import Types.Distribution
-import qualified BuildInfo
+import Assistant.Upgrade
 
 import qualified Data.Text as T
 import qualified System.FilePath.ByteString as P
@@ -59,7 +59,7 @@ prefsAForm d = PrefsForm
 		, ("disabled", NoAutoUpgrade)
 		]
 	autoUpgradeLabel
-		| isJust BuildInfo.upgradelocation = "Auto upgrade"
+		| upgradeSupported = "Auto upgrade"
 		| otherwise = "Auto restart on upgrade"
 
 	positiveIntField = check isPositive intField
diff --git a/CHANGELOG b/CHANGELOG
index e914ee55f6..fc0db5e3d0 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -13,6 +13,8 @@ git-annex (8.20201117) UNRELEASED; urgency=medium
     the stderr pipe to it was left open, due to a daemon having inherited
     the file descriptor.
   * Fix build on Windows.
+  * Prevent windows assistant from trying (and failing) to upgrade
+    itself, which has never been supported on windows.
 
  -- Joey Hess <id@joeyh.name>  Mon, 16 Nov 2020 09:38:32 -0400
 
diff --git a/doc/bugs/Upgrader_crashed.mdwn b/doc/bugs/Upgrader_crashed.mdwn
index 89fb403b15..b9b8238f41 100644
--- a/doc/bugs/Upgrader_crashed.mdwn
+++ b/doc/bugs/Upgrader_crashed.mdwn
@@ -37,3 +37,6 @@ Upgrader crashed: C:\Users\alexasus\.config\git-annex\program: openFile: does no
 I've barely just installed. So I'm gonna get going these days. That warning doesn't seem to be an issue so far. I've looked it up but couldn't find any other reports for that warning.
 
 
+
+> [[fixed|done]] (by skipping checking upgrades on OS's where it's not
+> supported) --[[Joey]]