diff --git a/src/qemu/qemu_block.c b/src/qemu/qemu_block.c
index 775c125467..3424ae5676 100644
--- a/src/qemu/qemu_block.c
+++ b/src/qemu/qemu_block.c
@@ -1163,7 +1163,10 @@ qemuBlockStorageSourceGetBackendProps(virStorageSourcePtr src,
         if (qemuBlockStorageSourceGetBlockdevGetCacheProps(src, fileprops) < 0)
             goto cleanup;
 
-        if (virJSONValueObjectAdd(fileprops, "b:read-only", src->readonly, NULL) < 0)
+        if (virJSONValueObjectAdd(fileprops,
+                                  "b:read-only", src->readonly,
+                                  "s:discard", "unmap",
+                                  NULL) < 0)
             goto cleanup;
     }