diff --git a/cmd/toolsrv/p9.go b/cmd/toolsrv/p9.go
index cb099b7..811368e 100644
--- a/cmd/toolsrv/p9.go
+++ b/cmd/toolsrv/p9.go
@@ -31,6 +31,7 @@ type fid struct {
 
 // authFid represents an auth file handle for Tauth.
 type authFid struct {
+	mu            sync.Mutex
 	uname         string
 	aname         string
 	authenticated bool
@@ -214,8 +215,10 @@ func handleAttach(cs *connState, fc *plan9.Fcall, tree *virtfs.Tree) *plan9.Fcal
 	if !hasAuth {
 		return errFcall(fc, "invalid afid")
 	}
-
-	if !af.authenticated {
+	af.mu.Lock()
+	authenticated := af.authenticated
+	af.mu.Unlock()
+	if !authenticated {
 		return errFcall(fc, "not authenticated")
 	}
 
@@ -238,19 +241,25 @@ func handleAuthWrite(cs *connState, fc *plan9.Fcall, af *authFid) *plan9.Fcall {
 		return errFcall(fc, err.Error())
 	}
 
+	af.mu.Lock()
 	af.authenticated = true
 	af.token = token
+	af.mu.Unlock()
 
 	return &plan9.Fcall{Type: plan9.Rwrite, Tag: fc.Tag, Count: uint32(len(fc.Data))}
 }
 
 // handleAuthRead handles reading the token from an auth fid.
 func handleAuthRead(cs *connState, fc *plan9.Fcall, af *authFid) *plan9.Fcall {
-	if !af.authenticated {
+	af.mu.Lock()
+	authenticated := af.authenticated
+	token := af.token
+	af.mu.Unlock()
+	if !authenticated {
 		return errFcall(fc, "write secret first")
 	}
 
-	data := []byte(af.token + "\n")
+	data := []byte(token + "\n")
 
 	offset := int(fc.Offset)
 	if offset >= len(data) {
@@ -573,14 +582,18 @@ func handleWrite(cs *connState, fc *plan9.Fcall, tree *virtfs.Tree) *plan9.Fcall
 	if !isFid {
 		return errFcall(fc, "unknown fid")
 	}
-	if !f.opened {
+	f.mu.Lock()
+	opened := f.opened
+	entry := f.entry
+	f.mu.Unlock()
+	if !opened {
 		return errFcall(fc, "not open")
 	}
-	if f.entry == nil {
+	if entry == nil {
 		return errFcall(fc, "no entry")
 	}
 
-	err := f.entry.Write(fc.Data)
+	err := entry.Write(fc.Data)
 	if err != nil {
 		return errFcall(fc, err.Error())
 	}