diff --git a/CHANGELOG b/CHANGELOG
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -1,3 +1,10 @@
+propellor (4.7.1) unstable; urgency=medium
+
+  * Added Mount.isMounted.
+  * Grub.bootsMounted: Bugfix.
+
+ -- Joey Hess <id@joeyh.name>  Fri, 28 Jul 2017 22:22:40 -0400
+
 propellor (4.7.0) unstable; urgency=medium
 
   * Add Apt.proxy property to set a host's apt proxy.
diff --git a/debian/changelog b/debian/changelog
--- a/debian/changelog
+++ b/debian/changelog
@@ -1,3 +1,10 @@
+propellor (4.7.1) unstable; urgency=medium
+
+  * Added Mount.isMounted.
+  * Grub.bootsMounted: Bugfix.
+
+ -- Joey Hess <id@joeyh.name>  Fri, 28 Jul 2017 22:22:40 -0400
+
 propellor (4.7.0) unstable; urgency=medium
 
   * Add Apt.proxy property to set a host's apt proxy.
diff --git a/propellor.cabal b/propellor.cabal
--- a/propellor.cabal
+++ b/propellor.cabal
@@ -1,5 +1,5 @@
 Name: propellor
-Version: 4.7.0
+Version: 4.7.1
 Cabal-Version: >= 1.20
 License: BSD2
 Maintainer: Joey Hess <id@joeyh.name>
diff --git a/src/Propellor/Property/Grub.hs b/src/Propellor/Property/Grub.hs
--- a/src/Propellor/Property/Grub.hs
+++ b/src/Propellor/Property/Grub.hs
@@ -132,7 +132,12 @@
 
 	cleanupmounts :: Property Linux
 	cleanupmounts = property desc $ liftIO $ do
-		umountLazy (inmnt "/sys")
-		umountLazy (inmnt "/proc")
-		umountLazy (inmnt "/dev")
+		cleanup "/sys"
+		cleanup "/proc"
+		cleanup "/dev"
 		return NoChange
+	  where
+		cleanup m = 
+			let mp = inmnt m
+			in whenM (isMounted mp) $
+				umountLazy mp
diff --git a/src/Propellor/Property/Mount.hs b/src/Propellor/Property/Mount.hs
--- a/src/Propellor/Property/Mount.hs
+++ b/src/Propellor/Property/Mount.hs
@@ -78,6 +78,10 @@
 mountPoints :: IO [MountPoint]
 mountPoints = lines <$> readProcess "findmnt" ["-rn", "--output", "target"]
 
+-- | Checks if anything is mounted at the MountPoint.
+isMounted :: MountPoint -> IO Bool
+isMounted mnt = isJust <$> getFsType mnt
+
 -- | Finds all filesystems mounted inside the specified directory.
 mountPointsBelow :: FilePath -> IO [MountPoint]
 mountPointsBelow target = filter (\p -> simplifyPath p /= simplifyPath target)
@@ -129,12 +133,15 @@
 
 -- | Unmounts a device or mountpoint,
 -- lazily so any running processes don't block it.
+--
+-- Note that this will fail if it's not mounted.
 umountLazy :: FilePath -> IO ()
 umountLazy mnt =  
 	unlessM (boolSystem "umount" [ Param "-l", Param mnt ]) $
 		stopPropellorMessage $ "failed unmounting " ++ mnt
 
--- | Unmounts anything mounted inside the specified directory.
+-- | Unmounts anything mounted inside the specified directory,
+-- not including the directory itself.
 unmountBelow :: FilePath -> IO ()
 unmountBelow d = do
 	submnts <- mountPointsBelow d