diff --git a/sbin/newfs_o2fs/newfs_o2fs.c b/sbin/newfs_o2fs/newfs_o2fs.c
index 0adf693..f12b08c 100644
--- a/sbin/newfs_o2fs/newfs_o2fs.c
+++ b/sbin/newfs_o2fs/newfs_o2fs.c
@@ -112,6 +112,7 @@ ObjID *AddFile(const char *file)
     ObjID *id = malloc(sizeof(ObjID));
     BNode node;
 
+    memset(id, 0, sizeof(*id));
     memset(&node, 0, sizeof(node));
     memcpy(node.magic, BNODE_MAGIC, 8);
     node.versionMajor = O2FS_VERSION_MAJOR;
@@ -209,6 +210,7 @@ ObjID *AddDirectory()
     int i;
     uint64_t off;
 
+    memset(id, 0, sizeof(*id));
     memset(&node, 0, sizeof(node));
     memcpy(node.magic, BNODE_MAGIC, 8);
     node.versionMajor = O2FS_VERSION_MAJOR;
@@ -262,6 +264,9 @@ int main(int argc, char * const *argv)
     int ch;
     int status;
 
+    // Sanity check
+    assert(sizeof(BDirEntry) == 512);
+
     struct option longopts[] = {
 	{ "manifest",		required_argument,	NULL,	'm' },
 	{ "size",		required_argument,	NULL,	's' },