diff --git a/libao/libao-async.rkt b/libao/libao-async.rkt
index 0b73753..0d45261 100644
--- a/libao/libao-async.rkt
+++ b/libao/libao-async.rkt
@@ -196,10 +196,14 @@
       (begin
         (displayln "Pausing ao play thread")
         (os-semaphore-wait (ao-shm-pause-sem shm))
-        (set-ao-shm-paused! shm pause))
+        (mutex-lock (ao-shm-mutex shm))
+        (set-ao-shm-paused! shm pause)
+        (mutex-unlock (ao-shm-mutex.shm)))
       (begin
         (displayln "Continuing ao play thread")
+        (mutex-lock (ao-shm-mutex shm))
         (set-ao-shm-paused! shm pause)
+        (mutex-unlock (ao-shm-mutex.shm))
         (os-semaphore-post (ao-shm-pause-sem shm)))
       )
   )