1 files changed, 7 insertions, 2 deletions
diff --git a/qemu-img.c b/qemu-img.c
index 7956a89..7c4fc60 100644
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -2508,8 +2508,10 @@ static int img_convert(int argc, char **argv)
 
     if (out_baseimg_param) {
         if (!qemu_opt_get(opts, BLOCK_OPT_BACKING_FMT)) {
-            warn_report("Deprecated use of backing file without explicit "
-                        "backing format");
+            error_report("Use of backing file requires explicit "
+                         "backing format");
+            ret = -1;
+            goto out;
         }
     }
 
@@ -3765,6 +3767,9 @@ static int img_rebase(int argc, char **argv)
     if (ret == -ENOSPC) {
         error_report("Could not change the backing file to '%s': No "
                      "space left in the file header", out_baseimg);
+    } else if (ret == -EINVAL && out_baseimg && !out_basefmt) {
+        error_report("Could not change the backing file to '%s': backing "
+                     "format must be specified", out_baseimg);
     } else if (ret < 0) {
         error_report("Could not change the backing file to '%s': %s",
             out_baseimg, strerror(-ret));