diff --git a/src/libCom/freeList/freeListLib.c b/src/libCom/freeList/freeListLib.c
index 3ddd1331c..5e07ba9c3 100644
--- a/src/libCom/freeList/freeListLib.c
+++ b/src/libCom/freeList/freeListLib.c
@@ -148,6 +148,10 @@ epicsShareFunc void epicsShareAPI freeListCleanup(void *pvt)
 epicsShareFunc size_t epicsShareAPI freeListItemsAvail(void *pvt)
 {
     FREELISTPVT *pfl = pvt;
-    return pfl->nBlocksAvailable;
+    size_t nBlocksAvailable;
+    epicsMutexMustLock(pfl->lock);
+    nBlocksAvailable = pfl->nBlocksAvailable;
+    epicsMutexUnlock(pfl->lock);
+    return nBlocksAvailable;
 }