diff --git a/reactos/drivers/filesystems/fastfat/fcb.c b/reactos/drivers/filesystems/fastfat/fcb.c
index 0b5f24a345b..c698ba72efe 100644
--- a/reactos/drivers/filesystems/fastfat/fcb.c
+++ b/reactos/drivers/filesystems/fastfat/fcb.c
@@ -292,6 +292,8 @@ vfatGrabFCB(
     PDEVICE_EXTENSION pVCB,
     PVFATFCB pFCB)
 {
+    ASSERT(ExIsResourceAcquiredExclusive(&pVCB->DirResource));
+
     ++pFCB->RefCount;
 }
 
@@ -305,6 +307,8 @@ vfatReleaseFCB(
     DPRINT("releasing FCB at %p: %wZ, refCount:%d\n",
            pFCB, &pFCB->PathNameU, pFCB->RefCount);
 
+    ASSERT(ExIsResourceAcquiredExclusive(&pVCB->DirResource));
+
     while (pFCB)
     {
         pFCB->RefCount--;