diff --git a/src/hb-mutex-private.hh b/src/hb-mutex-private.hh
index be0f68768..24b6d9ac3 100644
--- a/src/hb-mutex-private.hh
+++ b/src/hb-mutex-private.hh
@@ -100,6 +100,7 @@ struct hb_mutex_t
 struct hb_static_mutex_t : hb_mutex_t
 {
   hb_static_mutex_t (void)  { this->init (); }
+  ~hb_static_mutex_t (void) { this->free (); }
 
   private:
   NO_COPY (hb_static_mutex_t);