diff --git a/libguestfs.spec b/libguestfs.spec
index f4f7c3a..c5c0e5d 100644
--- a/libguestfs.spec
+++ b/libguestfs.spec
@@ -336,8 +336,8 @@ virtual machines.
 export vmchannel_test=no
 export QEMU=/usr/bin/qemu-kvm
 # for configure macro below
-CFLAGS="$RPM_OPT_FLAGS -Wno-unused"
-CXXFLAGS="$RPM_OPT_FLAGS -Wno-unused"
+CFLAGS="$RPM_OPT_FLAGS -Wno-unused -DGUESTFS_QEMU_NO_VIRTIO_BLK"
+CXXFLAGS="$RPM_OPT_FLAGS -Wno-unused -DGUESTFS_QEMU_NO_VIRTIO_BLK"
 autoreconf -fi
 %configure \
 	--help || :