diff --git a/internal/lockedfile/internal/filelock/filelock.go b/internal/lockedfile/internal/filelock/filelock.go
index d373318..f0452f0 100644
--- a/internal/lockedfile/internal/filelock/filelock.go
+++ b/internal/lockedfile/internal/filelock/filelock.go
@@ -8,7 +8,6 @@
 package filelock
 
 import (
-	"errors"
 	"io/fs"
 )
 
@@ -74,10 +73,3 @@ func (lt lockType) String() string {
 		return "Unlock"
 	}
 }
-
-// IsNotSupported returns a boolean indicating whether the error is known to
-// report that a function is not supported (possibly for a specific input).
-// It is satisfied by errors.ErrUnsupported as well as some syscall errors.
-func IsNotSupported(err error) bool {
-	return errors.Is(err, errors.ErrUnsupported)
-}
diff --git a/internal/lockedfile/lockedfile.go b/internal/lockedfile/lockedfile.go
index 8bd2ffb..f48124f 100644
--- a/internal/lockedfile/lockedfile.go
+++ b/internal/lockedfile/lockedfile.go
@@ -94,6 +94,11 @@ func (f *File) Close() error {
 
 	err := closeFile(f.osFile.File)
 	f.cleanup.Stop()
+	// f may be dead at the moment after we access f.cleanup,
+	// so the cleanup can fire before Stop completes. Keep f
+	// alive while we call Stop. See the documentation for
+	// runtime.Cleanup.Stop.
+	runtime.KeepAlive(f)
 	return err
 }