diff --git a/blockdev-nbd.c b/blockdev-nbd.c
index c76d5416b9..d73ac1b026 100644
--- a/blockdev-nbd.c
+++ b/blockdev-nbd.c
@@ -146,6 +146,7 @@ void qmp_nbd_server_add(const char *device, bool has_name, const char *name,
     BlockDriverState *bs = NULL;
     BlockBackend *on_eject_blk;
     NBDExport *exp;
+    int64_t len;
 
     if (!nbd_server) {
         error_setg(errp, "NBD server not running");
@@ -168,6 +169,13 @@ void qmp_nbd_server_add(const char *device, bool has_name, const char *name,
         return;
     }
 
+    len = bdrv_getlength(bs);
+    if (len < 0) {
+        error_setg_errno(errp, -len,
+                         "Failed to determine the NBD export's length");
+        return;
+    }
+
     if (!has_writable) {
         writable = false;
     }
@@ -175,7 +183,7 @@ void qmp_nbd_server_add(const char *device, bool has_name, const char *name,
         writable = false;
     }
 
-    exp = nbd_export_new(bs, 0, -1, name, NULL, bitmap,
+    exp = nbd_export_new(bs, 0, len, name, NULL, bitmap,
                          writable ? 0 : NBD_FLAG_READ_ONLY,
                          NULL, false, on_eject_blk, errp);
     if (!exp) {
diff --git a/nbd/server.c b/nbd/server.c
index 6b136019f8..51ee8094e0 100644
--- a/nbd/server.c
+++ b/nbd/server.c
@@ -1495,17 +1495,13 @@ NBDExport *nbd_export_new(BlockDriverState *bs, off_t dev_offset, off_t size,
     exp->refcount = 1;
     QTAILQ_INIT(&exp->clients);
     exp->blk = blk;
+    assert(dev_offset >= 0 && dev_offset <= INT64_MAX);
     exp->dev_offset = dev_offset;
     exp->name = g_strdup(name);
     exp->description = g_strdup(description);
     exp->nbdflags = nbdflags;
-    exp->size = size < 0 ? blk_getlength(blk) : size;
-    if (exp->size < 0) {
-        error_setg_errno(errp, -exp->size,
-                         "Failed to determine the NBD export's length");
-        goto fail;
-    }
-    exp->size -= exp->size % BDRV_SECTOR_SIZE;
+    assert(size >= 0 && size <= INT64_MAX - dev_offset);
+    exp->size = QEMU_ALIGN_DOWN(size, BDRV_SECTOR_SIZE);
 
     if (bitmap) {
         BdrvDirtyBitmap *bm = NULL;