diff --git a/drivers/zero.c b/drivers/zero.c
index 9799517..a01bbe1 100644
--- a/drivers/zero.c
+++ b/drivers/zero.c
@@ -19,6 +19,9 @@ static int zeroClose(struct uAddrVirtualReg *vreg)
 {
     struct zeroMappedEntry *ent = (struct zeroMappedEntry *)vreg->res->customData;
     ent->refCnt--;
+    if (ent->refCnt == 0) {
+        free(vreg->res->customData);
+    }
     return 0;
 }