diff --git a/block/copy-before-write.c b/block/copy-before-write.c
index b866e42271d0c7553b6951da12b7d6d88f21de4a..9a0e2b69d911633f53aaca48b4b5374f12f9e07e 100644
--- a/block/copy-before-write.c
+++ b/block/copy-before-write.c
@@ -503,7 +503,7 @@ static void cbw_close(BlockDriverState *bs)
     s->bcs = NULL;
 }
 
-BlockDriver bdrv_cbw_filter = {
+static BlockDriver bdrv_cbw_filter = {
     .format_name = "copy-before-write",
     .instance_size = sizeof(BDRVCopyBeforeWriteState),
 
diff --git a/block/preallocate.c b/block/preallocate.c
index 4d821250366ed33299fc99a4e1e75f749e53fd87..3d0f621003916cb57ff9f5b652fc6d81ce7e4d56 100644
--- a/block/preallocate.c
+++ b/block/preallocate.c
@@ -535,7 +535,7 @@ static void preallocate_child_perm(BlockDriverState *bs, BdrvChild *c,
     }
 }
 
-BlockDriver bdrv_preallocate_filter = {
+static BlockDriver bdrv_preallocate_filter = {
     .format_name = "preallocate",
     .instance_size = sizeof(BDRVPreallocateState),
 
diff --git a/block/snapshot-access.c b/block/snapshot-access.c
index 67ea339da992835dcc46f3384945a48117d3da82..8d4e8932b8abe5f9c0e47450c2f511f00cf27e61 100644
--- a/block/snapshot-access.c
+++ b/block/snapshot-access.c
@@ -108,7 +108,7 @@ static void snapshot_access_child_perm(BlockDriverState *bs, BdrvChild *c,
     *nshared = BLK_PERM_ALL;
 }
 
-BlockDriver bdrv_snapshot_access_drv = {
+static BlockDriver bdrv_snapshot_access_drv = {
     .format_name = "snapshot-access",
 
     .bdrv_open                  = snapshot_access_open,