diff --git a/ipn/store.go b/ipn/store.go
index 84ae00dd2..550aa8cba 100644
--- a/ipn/store.go
+++ b/ipn/store.go
@@ -72,6 +72,7 @@ func CurrentProfileKey(userID string) StateKey {
 }
 
 // StateStore persists state, and produces it back on request.
+// Implementations of StateStore are expected to be safe for concurrent use.
 type StateStore interface {
 	// ReadState returns the bytes associated with ID. Returns (nil,
 	// ErrStateNotExist) if the ID doesn't have associated state.