diff --git a/block/backup.c b/block/backup.c
index f8309be01b..f704c83a98 100644
--- a/block/backup.c
+++ b/block/backup.c
@@ -576,6 +576,10 @@ BlockJob *backup_job_create(const char *job_id, BlockDriverState *bs,
     assert(bs);
     assert(target);
 
+    /* QMP interface protects us from these cases */
+    assert(sync_mode != MIRROR_SYNC_MODE_INCREMENTAL);
+    assert(sync_bitmap || sync_mode != MIRROR_SYNC_MODE_BITMAP);
+
     if (bs == target) {
         error_setg(errp, "Source and target cannot be the same");
         return NULL;
@@ -607,16 +611,7 @@ BlockJob *backup_job_create(const char *job_id, BlockDriverState *bs,
         return NULL;
     }
 
-    /* QMP interface should have handled translating this to bitmap mode */
-    assert(sync_mode != MIRROR_SYNC_MODE_INCREMENTAL);
-
     if (sync_mode == MIRROR_SYNC_MODE_BITMAP) {
-        if (!sync_bitmap) {
-            error_setg(errp, "must provide a valid bitmap name for "
-                       "'%s' sync mode", MirrorSyncMode_str(sync_mode));
-            return NULL;
-        }
-
         /* If we need to write to this bitmap, check that we can: */
         if (bitmap_mode != BITMAP_SYNC_MODE_NEVER &&
             bdrv_dirty_bitmap_check(sync_bitmap, BDRV_BITMAP_DEFAULT, errp)) {
diff --git a/blockdev.c b/blockdev.c
index 210226d829..f889da0b42 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -3529,6 +3529,16 @@ static BlockJob *do_backup_common(BackupCommon *backup,
         return NULL;
     }
 
+    if ((backup->sync == MIRROR_SYNC_MODE_BITMAP) ||
+        (backup->sync == MIRROR_SYNC_MODE_INCREMENTAL)) {
+        /* done before desugaring 'incremental' to print the right message */
+        if (!backup->has_bitmap) {
+            error_setg(errp, "must provide a valid bitmap name for "
+                       "'%s' sync mode", MirrorSyncMode_str(backup->sync));
+            return NULL;
+        }
+    }
+
     if (backup->sync == MIRROR_SYNC_MODE_INCREMENTAL) {
         if (backup->has_bitmap_mode &&
             backup->bitmap_mode != BITMAP_SYNC_MODE_ON_SUCCESS) {