diff --git a/src/qemu/qemu_conf.c b/src/qemu/qemu_conf.c
index 0cbedf257d3e8fb5f50027ef0bbf9d0c8431f960..355fdb9a1e310a21e71547872bbdb3b121ba02bb 100644
--- a/src/qemu/qemu_conf.c
+++ b/src/qemu/qemu_conf.c
@@ -2479,7 +2479,7 @@ qemuBuildDriveStr(virDomainDiskDefPtr disk,
     if (disk->readonly &&
         qemuCmdFlags & QEMUD_CMD_FLAG_DEVICE)
         virBufferAddLit(&opt, ",readonly=on");
-    if (disk->driverType &&
+    if (disk->driverType && *disk->driverType != '\0' &&
         disk->type != VIR_DOMAIN_DISK_TYPE_DIR &&
         qemuCmdFlags & QEMUD_CMD_FLAG_DRIVE_FORMAT)
         virBufferVSprintf(&opt, ",format=%s", disk->driverType);